Battle of Atlantic , Black May - Michael Gannon


Winter—Spring 1943

The Battle of the Atlantic was the dominating factor all through the war. Never for one moment could we forget that everything happening elsewhere, on land, at sea, or in the air, depended ultimately on its outcome, and amid all other cares we viewed its changing fortunes day by day with hope or apprehension.


The decisive point in warfare against England lies in attacking her merchant shipping in the Atlantic.


Whatever efforts are made by the land armies, the Navy must have the casting vote in the present contest.


IN THE FIRST DARK HOURS of the first day of the forty-fifth month of the longest armed struggle of World War II—the Battle of the Atlantic—134 submarines of the German underseas fleet (U-Bootwaffe) were at sea, of which 118 were on or proceeding to operational stations in the North Atlantic Ocean, where, 58 were already deployed in four battle groups. Most of the U-boats, as they were called, had sortied from French bases on the Bay of Biscay, the remainder from bases on the Baltic Sea, from which they rounded the north of Scotland. It was the largest number assembled at sea to that date in the war, I May 1943. Steel-gray spectral presences, they made an ominous murmuring across the deep, as of the gathering of a host, on the eve of a titanic trial of strength. At issue was control of the ocean’s merchant shipping lanes. The enemy was Great Britain’s Royal Navy and Royal Air Force, helped by forces of the United States and Canada. Most of the U-boats were ordered to form patrol lines across the expected routes of warship-guarded transatlantic convoys of freighters and tankers that sailed between North America and the British Isles. Others watched for north-south coastwise convoys or for independently sailing vessels along the shores of Spain and West Africa, or for shipping inside the Mediterranean Sea.

Armed with the most recent types of destructive torpedoes, all the Atlantic boats were under the same general order from Grossadmiral Karl Dönitz, Commander-in-Chief of the German Navy (Kriegsmarine) and Flag Officer, U-Boats: Angreifen! Ran! Versenken!—Attack! Advance! Sink! Their purpose in the transatlantic sea lanes: destroy British and American vessels that, through their deliveries of food, fuel, ferrous and nonferrous metals, other raw materials, and finished weapons, were keeping Great Britain in the war, and making possible a future Allied cross-Channel invasion of German-occupied Europe. As April gave way to May 1943, the Allied defensive war against the U-boat was perceived by many in London and Washington, if not in Moscow, as the single most important campaign of World War II, for upon its outcome rested the success or failure of the Allies’ strategies in all other theaters of operation. This was so because victory in Western Europe depended on uninterrupted sea communications across the North Atlantic, which provided aid to the Soviet ally as well as to the British (although Arctic convoys to Murmansk and Archangel had been suspended since March because of the growing crisis in the Atlantic), and because the Allied strategic assumption was that the defeat of Germany ensured the defeat of Japan, but not the converse.


Admiral Karl Donitz

Put in the simplest terms, Admiral Dönitz and his U-boats were engaged in a tonnage battle (Tonnageschlacht) with Allied trade, that is, in a campaign to sink more British and American merchant ship tonnage than the Allies could replace with new construction. Dönitz and his staff had calculated in 1940 that in order to accomplish that attrition, his boats (with surface raiders, aircraft, and mines accounting for a small percentage of the total) would have to inflict a monthly loss rate of 700,000 Gross Register Tons (GRT). If successful, Britain’s armed forces, industries, and people would be strangled or starved into submission. The British had estimated that 600,000 would be enough to do them in. But so far, by either measure, Dönitz was not winning that battle. Operating during the first half of 1942 in poorly defended waters off the United States East and Gulf coasts and in the Caribbean Basin, the best that he had done was 125 ships for 584, 788 GRT, of which only 10 percent was convoyed, in May 1942; and 131 ships for 616, 904 GRT, of which only 12 percent was convoyed, in June 1942. The best that he had done where most of the merchant traffic was convoyed under warship and aircraft protection was 118 ships for an impressive (and record) 743, 321 GRT, in November 1942. The numbers fell off in the following three months.

Then, in the first twenty days of March 1943, his sharks had gone on another feeding frenzy, sinking seventy-two vessels, sixty of them in fourteen Royal Navy—protected convoys. Twenty-two of the ship losses came on 16–20 March during an attack by three U-boat groups code-named Raubgraf (Robber Baron), consisting of eight boats; Stürmer (Go-Getter), eighteen boats; and Dränger (Pusher), eleven boats, with several other independently operating boats, against three convergent transatlantic eastbound convoys identified by the Allies as SC.122, HX.229, and HX.229A, with a combined 125 merchant ships in orderly columns. The three convoy formations had been protected during their passage by nine destroyers, three frigates, four sloops, nine corvettes, and two cutters, and at various times by fifty-one Royal Air Force and Royal Canadian Air Force aircraft. German radio broadcasts called the engagement “the greatest convoy battle of all time,” based on the number and tonnage of ships claimed as sunk for the loss of only one attacker (U-384). Allied tonnage lost to U-boats in the month by 20 March amounted to 443, 951 GRT. Had sinkings continued at that same pace for the remainder of the month, which they did not, the tonnage harvested (688, 124 GRT) would have approached November’s record and would have exceeded the original British minimum calculated for a decisive guerre de course. The actual monthly total was 105 ships for 590, 234 GRT. And more to the point, by spring 1943 neither number would have matched the minimum tonnage now required to keep pace with replacement construction from America’s unexpectedly productive ninety-nine shipyards. The bar on the high jump had been raised to 1.3 million GRT.

Still, the numbers for March, particularly the losses from SC.122 and HX.229—HX.229A was unharmed—were of a magnitude to set off alarm bells in the Anti-U-Boat Division of the Naval Staff at the British Admiralty at Whitehall, London, the district where many government departments are located and a term frequently used as a synonym for Admiralty. In language committed to writing well after the convoy disaster, one senses the consternation that reputedly swept certain corridors of Whitehall at the time. Though the convoy system had proved in two world wars to be the keystone of Britain’s trade protection, for the first time in the second war there were doubters. “It appeared possible,” the Anti-U-Boat Division reflected, “that we should not be able to continue [to regard] convoy as an effective system of defence.” In a watershed expression, the Admiralty is alleged to have conceded, “The Germans never came so near to disrupting communication between the New World and the Old as in the first twenty days of March 1943.” Captain Stephen W. Roskill, R.N. (Royal Navy), official historian of Royal Navy operations in World War II, stated in 1956: “Nor can one yet look back on that month without feeling something approaching horror over the losses we suffered.”

One could have countered that there was no need for these expressions, since American shipyards were producing such prodigious numbers of replacement hulls, new Allied “bottoms” had already exceeded in the preceding fall any destruction that the U-boats were then inflicting; further, that 90 percent of all ships in convoys attacked by U-boats were getting through to port safely, even 82 percent of hard-hit SC.122/HX.229. Indeed, well-hidden in the bowels of the “Citadel,” a concrete blockhouse on the northwest corner of Whitehall, two relatively junior reserve officers held the contrary and optimistic view that U-boat fortunes were in constant and inevitable decline. A mere glance at the graphs that covered the walls of their Submarine Tracking Room of the Admiralty’s Operational Intelligence Centre (OIC) was enough to persuade Tracking Room director Temporary Commander Rodger Winn, R.N.V.R., Special Branch, and his deputy, Lieutenant Patrick Beesly, R.N.V.R., that most of the relevant numbers were going Britain’s way: shipping losses alongside replacements; U-boat groups alongside Allied escort vessels and aircraft; U-boat equipment alongside new Allied weapons and detection devices.

But if we may believe the official history, their careful optimism seems not to have passed persuasively up and across to the Anti-U-Boat Division, whose attention, we are led to believe, was focused on quite a different set of facts: (1) that the Germans had the largest U-boat strength yet seen in the Atlantic war; (2) that U-boat construction still exceeded casualties; (3) that 84 percent of the ships sunk in March were sunk while in protected convoy; and (4) that from an average of 39 percent of ships sunk in convoy during the second half of 1942, the average toll for the first quarter of 1943 had risen to a startling 75 percent. Captain Roskill expressed the worry: “Where could the Admiralty turn if the convoy system had lost its effectiveness? They did not know; but they must have felt, though no one admitted it, that defeat then stared them in the face.” Would the U-boats succeed at last in severing Britain’s lifeline and winning the Atlantic—perhaps the war?

Those fears, amply expressed in the official history written thirteen years later, were not discovered by this writer in any of the documentation from the immediate post-20 March period as far as January 1944. That includes the Most Secret minutes of the War Cabinet Anti-U-boat Warfare Committee (A.U. Committee), the highest deliberative body to be concerned with such matters. Those fears would seem to be overwrought at best and irrational at worst, assuming that they were actually uttered by Admiralty authorities, as reported. Indeed, on 30 March, in a document prepared for the A.U. Committee, the First Sea Lord, Admiral of the Fleet Sir Dudley Pound, spoke with cautious optimism about anti-U-boat prospects in the months immediately ahead. For one thing, he told the Prime Minister and members of that body, the heavy winter weather, which had caused so many merchant ship stragglers from convoys and had hampered the Navy’s high-frequency direction-finding equipment (receivers and antennas that tracked radio transmission from U-boats), was moderating. Second, both Support Groups (destroyers and other warships detailed to reinforce the close escorts of threatened convoys at sea) and auxiliary aircraft carriers had been freed up from operations in the Mediterranean and in North Russian waters, and were now being redeployed in the North Atlantic convoy lanes. Third, and most important, a significant number of new land-based aircraft were becoming available for Atlantic escort patrol. Thus, from the First Sea Lord, no Admiralty hand-wringing here!

And His Lordship might well have added that while during 1942 the at-sea loss exchange rate was 45,000 tons of merchant shipping sunk per U-boat lost, during the first quarter of 1943 the rate had fallen to 28,000 tons per U-boat lost. Other restorative tonics could be found in the facts that during the same first quarter, 270 more merchant ships in convoy made safe and timely arrivals at their destinations than had done so during the last three months of 1942; more U-boats (19) had been sunk in February than in any previous month of the war, and even in woeful March the figures for new shipping construction exceeded sinkings by 300,000 tons. It would seem that the despondency theme voiced by certain members of the Naval Staff s Anti-U-Boat Division and repeated in the Admiralty’s official history as well as in much of the historical literature since 1956 did not represent the Admiralty’s position and at this date deserves to be consigned overside in a weighted bag.

But if they did indeed waver, Their Lordships might have been emboldened in the faith did they know that statistical analyses done by the German Naval War Staff in Berlin at the same time revealed that the tonnage numbers credited to each U-boat per day at sea had been erratic and generally down since the preceding November. In that previously noted record month, the average per boat at sea number for the month was 329 GRT. In December it was 139. In January 1943 it was 129; in February 148; and in March 230. By those numbers, for the U-Bootwaffe to meet the new tonnage minimum of 1.3 million GRT (of which Donitz may well have been unaware: the Naval Intelligence Division figure given him in 1943 was 900,000 GRT per month) it would have to place at sea no fewer than 433 boats—nearly three and a quarter times the current figure—which was not possible anytime soon given German shipyard production of 19 boats per month, which barely exceeded the monthly loss rate in combat. For the present, a 1.3 million GRT achievement would have to come from greatly increased efficiency in each boat per sea-day, or from a collapse of British escort protection, or both. Neither seemed likely.

In any event, the stage was set in April for a decisive collision of the forces at sea, when Whitehall expected that, once refitted in Biscay bases from their exertions of March, the U-boats would return to the convoy lanes with even greater strength than that seen in the month before. If the ides of March was bad, that of April might be worse. As it happened, though, April was not the cruelest month at all. Sinkings by U-boats actually went down, to forty-eight ships for 276, 517 GRT, which was 47 percent of the March losses. And the U-boat per day at sea number was a low 127 GRT estimated, 76 actual.

One reason was a declining number of operational U-boats on North Atlantic stations, owing to longer-than-expected refit time at the Biscay bases, where many boats in need of repair, fuel, food, and armament replenishment had to lie for days in vulnerable berths outside the bombproof service and repair bunkers. By the ides of April (13 April), only thirty-three boats were on operations, and only one battle group, code-named Meise (Tit, a small European bird of the family Paridae), was formed, northeast of Cape Race, Newfoundland. Admiral Dönitz’s U-Boat Headquarters (called BdU, from Befehlshaber der Unterseeboote [Commander-in-Chief, U-Boats]) in Berlin considered the problem in its war diary for 16 April:

“Convoy warfare in March has led to a considerable wearing down of U-boats. A large number of boats have returned owing to fuel and torpedo exhaustion and damage. The gaps thus produced must be filled as quickly as possible, if the monthly sinking figures are to be increased. On 6 April, therefore, all boats of Type IX [large, longdistance IXB and IXC boats not normally employed in convoy operations] about to put out were ordered to proceed to the North Atlantic in order to make up the number of U-boats needed there to intercept convoys”


Not until the latter part of the month was the U-Bootwaffe able to dispatch a sizable fresh stream of boats, and so provide the numbers at sea on 1 May given at the beginning of this prologue. Sinkings of merchant ships declined for another reason as well, namely the larger number and effect of Allied convoy escorts, both surface and air, that Britain was able to deploy at sea in this month. Thus, though eleven convoys were attacked in the month, and all sustained losses for a total of twenty-nine sinkings, a stronger force of Allied ocean escorts, which included new “Support Groups” of emergency-directed escort warships and two auxiliary aircraft carriers, repeatedly drove off the German attackers and sank fifteen of their number, seven in the last week of the month. (U-boats sank twelve independently routed merchant ships in April.) Ten eastbound (234 ships) and nine westbound (182 ships) Atlantic convoys reached their destinations without interception.

There also appears to have been either an unaccountable decline of U-boat aggressiveness during the month, or else a surge in OIC Tracking Room wishful thinking on the subject, since it is here that one first reads an expression that is repeated in various British documents composed in the months thereafter: “It was in April that, for the first time, the U-boat groups failed to press home attacks even when favorably situated to do so.” The “failure to press” was detected during Commander Winn’s analysis of decrypted wireless (radio) transmissions between the U-boats and their headquarters, particularly with respect to the traffic’s frequent mention of Allied aircraft, whose number and threat had increased. “The outstanding impression felt on reading recent U-boat traffic,” Winn observed, “is that the spirit of the crews which are at present out on operations in the North Atlantic is low and general morale is shaky.”

If true that there was such a holding back, it is difficult to understand why such caution would be credited to a lack of will or morale. There certainly may have been sinking feelings—even despondency— at Berlin, where officers studied doleful statistics; but if Royal Navy frontline morale had not cracked under the unremitting strain of three and a half years of convoy losses, it is hard to conceive that U-boat ranks and ratings (officers and enlisted men), just off a staggering triumph at sea, would have lost heart simply because they sighted additional numbers of aircraft, or because they were failing to keep up with the exceptional sinking rate of the month before, while suffering, it should be added, no more U-boat losses (15) in April than they did in March. Vizeadmiral Horst von Schroeter, who as Oberleutnant zur See [hereafter Oblt.z. S.] commanded U-123 on operations during April, told this writer in December 1995 that morale remained high on his boat and that he noticed no special decline among other crews when he returned to base at Lorient. Were there, then, no “low spirits” as detected by Winn?

“I would like to say yes and no, because a lot of good friends of ours had gone down and had been lost. But, on the other hand, we had our duty. We had been in a war, in a world war; we had been soldiers, and we had to do our duty. I could imagine on our side in the minds of the Commanders there was some uncertainty because of the losses. They didn’t know what weapons the enemy had at hand, therefore they may have been more reluctant on pressing, on getting through. As for pessimism expressed in conversations with other Commanders at Lorient, I don’t remember such talking, because we more or less avoided talking about those things.”

If the Tracking Room observation was true that certain U-boats exhibited reluctance to attack targets with the expected dash and initiative, one likely reason was their reduced levels of command experience, owing to U-boat officer casualties that included not only Commanders but First (I.W.O.) and Second (II.W.O.) Watch Officers, who had merited their own boats. The BdU addressed this problem in its war diary for 7 April, and again near the end of the month, on the 25th, when it did a wash-up on a botched attempt by nineteen boats of the Meise group to operate against eastbound convoy HX.234 on 21–24 April: Noting conditions of “extremely changeable visibility” on the seas south of Greenland, the diary commented that, “The Commanders, for the most part inexperienced and fresh from home waters, were unable to cope with those conditions.” Yet, having said that much in mitigation of the Tracking Room’s interpretation, it is also true that BdU found reason, on 19 April, to admonish Commanders at sea for their lack of “warrior and fighter instincts.” This astonishing message, decrypted and read by the British, was occasioned by the apparent acceptance among some Commanders of a rumor that Allied escorts left depth charges, with timers, suspended from buoys:

“The enemy has based his defensive measures to a considerable extent on their morale effect. The man who allows his healthy warrior and fighter instincts to be hoaxed and humbugged ceases to have any appreciable powers of resistance to present-day enemy defenses. He is no longer capable of attack but feels universally hunted and persecuted.”

Whatever the meaning of April’s various mixed signals, it is enough to say that at month’s end the pendulum that had swung so far in Germany’s favor during March had returned by 30 April to center. For Dönitz the prognosis should have been clear: the tonnage battle was not winnable. Since the previous fall the figures for Allied merchant ship construction had passed and had continued to exceed with everincreasing plurality the figures for merchant ship losses; and by July 1943 the construction gains would overtake losses caused by U-boats plus all other enemy action, e.g., mines, aircraft bombs, surface raiders, and Schnellboote (S-boats, 105-foot fast torpedo boats). Despite growing evidence that his U-Bootwaffe lagged behind the curve, with little real chance of catching up, Dönitz persisted in talking as though the struggle for tonnage was still a war-winning strategy. Thus, on 11 April, to Adolf Hitler, at the Führers Berghof on the Obersalzburg near Berchtesgaden, in Bavaria, Dönitz pleaded that an increased allocation of 30,000 tons of steel be made to the U-boat yards in order to make possible a stepping-up of construction to twenty-seven boats per month. Hitler agreed with Dönitz’s argument, which included the following language:

“Submarine warfare is difficult. However, it is obvious that the aim of sinking merchant ships must be to sink more than the enemy can build. If we do not reach this objective, the enemy would continue to suffer severely through loss of his material substance, but we would not be successful in bleeding him to death due to the diminution of his tonnage. I therefore fear that the submarine war will be a failure if we do not sink more ships than the enemy is able to build.”

In continuing to promote the tonnage battle, Dönitz may well have thought that his boats and crews were capable of mounting one last transcendent effort, which, while it could not hope to reverse the merchant ship replacement gains, would at least make the rate of ship and cargo losses in convoy unacceptably high to the Allies. If such an effort could be uncoiled and sustained for a month’s period—here one can only speculate about his intentions and expectations—perhaps Britain would give up on convoys and scatter her seaborne trade in independently routed vessels—a not unreasonable expectation if certain Admiralty reports and histories were believed. Against such unprotected shipping his U-boats could then prowl and strike at their ease (with one eye cocked for aircraft). Was this the Grand Admiral’s desperate hope? Would he now commit all his boats in one last throw of the dice? Spes contra spem?

Then, as though to confirm the plausibility of his continued faith in the tonnage battle, on the night of 30 April/I May a single German boat, U-515, commanded by thirty-three year-old Kapitänleutnant (hereafter Kptlt.) Werner Henke, carried off one of the most spirited and successful actions by a U-boat in the entire Atlantic campaign, sinking seven convoyed ships of 43,255 GRT in the space of eight hours and forty minutes, torpedoing four of them within six and a half minutes! Here certainly was a higher efficiency of boats and perhaps the beginning of a transcendent effort. If what Henke achieved at the opening of May could be extrapolated by his and other boats, at the same pace, until the end of May, Dönitz would have his 1.3 million GRT in a single month’s time.



May Day

Not only must every opportunity to attack be resolutely seized, but it would also be a grave error to depart from the principles which have been hammered into U-boat crews so hard and so frequently: “get to your position ahead just as quickly as you can, launch your attack just as soon as you can, exploit your opportunities at once and as fully as you can.” KARL DÖNITZ

Enemy submarines are to be called U-boats. The term “submarine” is to be reserved for Allied underwater vessels. U-boats are those dastardly villains who sink our ships, while submarines are those gallant and noble craft which sink theirs. WINSTON S. CHURCHILL

THE U-515 WAS ON HER THIRD operational patrol since the longrange Type IXC boat emerged from the yards of Deutsche Werft at Hamburg-Finkenwerder and Werner Henke raised the national flag and his Commander’s pennant above her conning tower at the Indienststellung, or formal commissioning, on 21 February 1942. After six months of workup and tactical exercises, she had made her maiden war patrol, and Henke’s first as a Kommandant, on 12 August-14 October 1942 off Trinidad and Tobago in the southeast Caribbean, netting ten Allied ships sunk, for a total of 52,807 GRT; a not-inconsiderable tally for a single cruise, even given the fact that Henke was operating against mostly independently routed ships in a weakly defended area. It was a score outdone by only a handful of German boats during the war, and matched by only one U.S. Navy submarine in the Pacific (U.S.S. Tang in June-July 1944).

The U-515’s second cruise, on 7 November 1942–6 January 1943, off Gibraltar and the Azores, resulted in only two sinkings, but one vessel was a Royal Navy destroyer depot ship, H.M.S. Hecla (10,850 tons), and the other a passenger liner-troopship, Ceramic (18,713 GRT). The loss of life from the two ships had been dreadful: 279 lost from 847 ranks and ratings on the former; all but one of 656 on the latter. By 30 April 1943, U-515’s third patrol, begun on 21 February, was already one of the longest of the war, and due to grow longer still. Operating off first the Azores and then Dakar in Senegal, on the bulge of West Africa, U-515’s third cruise, like the second, had been mostly a run of bad luck, with only two merchant trophies of 10,657 GRT to show for sixty-nine days of steaming—a poor individual tonnage rate per sea-day of 154 GRT.

The first sinking had come on the evening of 4 March while U-515 was northwest of the Azores. On a calm sea with little wind and good visibility, Henke sighted a large freighter proceeding independently at 15 knots on a course of 050° (degrees). He advanced on the surface toward the target. What happened next he described in his war diary (Kriegstagebuch, hereafter KTB):

“Double fan launch [Fächer] from [torpedo] Tubes II and IV. [Torpedo] speed 14 knots, range [to target] 1,200 meters. [Target’s] bows on right, bearing 80 degrees, [torpedo] depth 5 meters, running times 37 and 38 seconds. Two hits amidship and forward [but] the steamer doesn’t sink. Coup de grace [Fangschuss] from [stern] Tube VI, depth [set to run below the keel of the target] 9 meters, [torpedo warhead equipped] with Pi 2 [Pistole-2: a detonator designed to be activated by the magnetic field of a ship’s steel keel], running time 36 seconds. Hit toward the stern, in the engine room—a powerful explosion. The steamer sinks slowly on an even keel, transmits wireless signal. [Another] coup de grace, this time from Tube I. Depth 10 [meters] with Pi 2, running time 25 seconds. Hit forward—great explosion. Ship goes down after about 10 minutes.”

It’s the California Star at 8,300 GRT, [which was sailing] from New Zealand to England with butter, cheese, lard, and meat. The Second Officer was taken prisoner. The Captain and First Officer probably went down with their ship.2The California Star, which carried general cargo as well as food, was a motor ship of British registry. Fifty of her seventy-four men on board were killed, fatally wounded, or drowned. The sinking took place at latitude and longitude coordinates 42°32’N, 37°20’W. On 21 March and 1 April U-515 rendezvoused with two returning boats, U-106 (Kptlt. Hermann Rasch) and U-67 (Kptlt. Günther Müller-Stockheim), to take on fuel, provisions, and spare parts. Henke’s second success on this patrol came thirty-six days after the first, on 9 April, at night, while steaming off Dakar. This victim, the French motor ship Bamako, was a smallish 2,357 GRT, slightly overestimated by Henke:

“Advanced on a freighter of 3,500 GRT. Double fan launch from [stern] Tubes V and VI. [Target’s] speed 8.5 knots. [Torpedo] depths set to 3 and 4 meters. [Target’s] bows on right bearing 80 degrees. Range 800 meters. [Torpedo] running times 60 and 61 seconds. Hits fore and aft. Ship capsizes and sinks very quickly.”

Twenty of the ship’s thirty-seven crew and passengers went to watery graves at position 14°57’N, 17°15’W.

The wages of war were not only bottoms and cargoes—a reminder, if one were needed by affronted humanity, that the fragile tissue of men was no equal to the violent and deadly instruments that roamed the spring Atlantic seeking whom they might devour. In that connection, it bears mention that if there has been a general fault with histories of the Atlantic war it has been their tendency to concentrate on the uniformed fighting services of sea and air, while giving scant notice to the civilian British, American, and other Allied merchant seamen who experienced the most danger of U-boat attack at sea and suffered by far the most human casualties.

A summary of wartime losses in the British Merchant Navy makes the point: about 185,000 merchant seamen served aboard freighters, tankers, and motor ships, of whom 32,952, or 17 percent, lost their lives. That was a higher casualty rate than the 9.3 percent suffered during the war by the Royal Navy, the 9 percent by the Royal Air Force, and the 6 percent by the British Army. To the merchant seamen casualties must be added losses suffered by Royal Navy and Army Royal Regiment of Maritime Artillery gunners who served aboard most merchant vessels and were colloquially called D.E.M.S. ratings, after Defensively Equipped Merchant Ships.

Henke’s U-boat was a Type IXC Atlantikboot, an improved version of two earlier submarine models, IXB and IXA, which had been built in the late 1930s and 1940 to specifications close to those of a World War I boat, U—81. The IX series had been envisioned originally as command and control boats, in which tactical group (“pack”) leaders could direct operations at sea (an idea abandoned in late 1940); also as reconnaissance and mine-laying boats; and, finally, as long-range high-seas attack boats. In the last capacity, Types IXB and IXC boats had conducted immensely successful torpedo operations against Allied shipping as far distant as the United States East Coast, the Caribbean Basin, and the coast of West Africa.

Because of their large displacement (1,120 tons, surfaced) and wide, flat upper deck, the Type IX boats received the sobriquet Seekuh (sea cow), after aquatic herbivorous mammals like the manatee. The IXC was 76.8 meters (254 feet) in length—about 21 feet longer than today’s Boeing jumbo jet 747–400—and 6.8 meters (22¼, ft.) across the beam. Surfaced keel depth was 4.7 meters (15½. ft.). Its fuel bunkers, or tanks, had a capacity of 208 tons, allowing for a surface, as against submerged, range of 11,000 nautical miles at an economy speed of 12 knots. (The prior Type IXB, a series produced in fewer numbers, had a smaller fuel capacity by 43 tons and a surface range of 8,700 nautical miles.) Propelled on the surface by two 2,200-horsepower diesel engines (ninecylinder, four-cycle, supercharged, salt water-cooled) manufactured by Maschinenfabrik Augsburg-Nürnberg AG (MAN), the IXC was capable of 18.3 knots maximum speed (one knot was one nautical mile per hour, about 1.15 statute miles per hour); and it was on the surface, which surprises many modern readers, that U-boats of this period did most of their travel and fighting: The submerged attack by periscope was an exception rather than the rule. In truth, because it could not operate continually under water, the 1943 U-boat was a submersible rather than a genuine submarine. It launched its torpedoes in the manner of a motor torpedo boat, and dived only to avoid enemy ships and planes, to find relief from rough weather, or to make an occasional submerged attack in daylight. Submerged, it could make 7.3 knots maximum (except that in U-515’s case, top speed tested out at 7.46), which greatly reduced its maneuverability and effectiveness, particularly in convoy battles.

Underwater propulsion was provided by twin electric dynamotors (E-Maschinen), manufactured by Siemens-Schuckertwerke AG, each rated at 500 horsepower. Power was supplied by sixty tons of storage battery arrays distributed under the interior deck plates. Even at economy speed of four knots, a submerged boat would exhaust its battery power after 64 nautical miles (one nautical mile was about 1.15 statute miles). By clutching a diesel to a dynamotor, which served as a generator, the batteries could be recharged, but that lengthy procedure required that the boat surface. Another kind of power transfer was supplied by compressed air, the product of either diesel-driven Junkers air compressors or an electric compressor that the crew employed for blowing water from the ballast, or diving, tanks when the boat surfaced; for starting the diesels; and for launching torpedoes from their tubes. Like the storage batteries, the compressed air tanks were “topped up” each time the boat surfaced.

In exterior appearance the IXC had the general form of any other boat or ship. It presented a sharp-edged stem at the bow, a rounded hull, a flat upper deck bisected by a superstructure, in this case a conning tower, and a stern. The outer steel casing visible to the eye, which also enclosed the fuel bunkers and the ballast tanks, made the hull more efficient for surface travel. The heart of the U-boat’s architecture, however, could not be seen: it was the pressure hull, a long, narrow, cylindrical tube constructed of welded high-tensile steel plates 18.5 millimeters thick. This structure, resistant to fifteen atmospheres of water pressure when submerged, enclosed the U-boat’s crew and its engines, motors, compressors, controls, and torpedoes. The normal crew list of a Type IX included four officers and forty-four ratings, but occasionally, on particularly long patrols, the complement would be increased by one or two officers, additional ratings, and perhaps a cameraman-correspondent from the official news service Propaganda-Kompanie or a physician. In those cases, the interior of the boat on departure, already constricted by food stores and reserve torpedoes, would be so cramped as almost to prevent human movement.

While the IX boats had the distinct advantage of long-range war waging, and while they performed well against independently sailing or weakly escorted vessels in distant coastal waters, where, in fact, the IXB sank more tonnage per boat than did any other U-boat type in the war, and individual IX boats became the third through sixth most productive of the war, they were at a marked disadvantage in the heavily escorted transatlantic sea lanes, where Britain’s seaborne trade moved in tight convoy columns protected by Royal Navy close escorts— destroyers, sloops, frigates, and corvettes—as well as by aircraft, both land-based and, from March 1943, escort carrier-based. The IXs had several particular problems that made them less suitable for convoy operations than another U-boat type that was three times more numerous in the Atlantic at this date, namely, the Type VII.

How well-regarded this latter type was by Dönitz and his boat commanders in convoy operations is evidenced by the fact that prior to and during the war 709 VIIs were manufactured and delivered to the U-Bootwaffe (as against 159 IXAs, IXBs, IXCs, and IXC/405), of which 665 were VIICs or VIIC/415. Produced in greater numbers than any other design in submarine history, the VIIC boat was arguably the best-integrated combat system developed by German engineers prior to the Type XXI, described later. Smaller than the IX, with a lower silhouette, more maneuverable both on the surface and underwater, the whippetlike VII dived faster than the IX, putting 13 meters (42.6 feet) of water above the hull in thirty seconds, while the larger IX required thirty-five seconds at best to do the same. As has been calculated, during that five seconds’ difference an Allied anti-submarine aircraft such as a Consolidated B-24 Liberator could close a target more than a third of a mile on a depth-bomb attack.6 Furthermore, underwater, the VII boats were more stable in maintaining depth and, because of their smaller size, were less easily located by British detection gear.

During March and April 1943 it was observed by BdU (U-Boat Headquarters) that the losses of IX boats to Allied escorts in the Atlantic was proportionately much higher than the losses of VIIs, leading to a decision on 5 May: “Type IXC boats leaving French ports are to be detailed to remote western or southern operational areas.” The same observation explains why it was such a radical step a month before, on 6 April, for BdU to direct IXs “to proceed to the North Atlantic in order to make up the number of U-boats needed there to intercept convoys”; and why the commitment of those resources had to be quickly reversed: though making up less than a quarter of the Atlantic force in April, the IXs suffered twice as many losses (8 to 4) as did the VIIs. Never enthusiastic about the IXs as a U-boat type, Dönitz had energetically opposed the construction figures that the Naval Staff in Berlin had advanced for them. Nonetheless, during the January-July 1942 offensive off the American coast (chapter 3) he had to have been thankful that he had as many IXs as he did, for the longdistance boats accounted for two-thirds of the merchant traffic sunk in those waters.

Essentially, a U-boat’s pressure hull existed as a weapons platform, that is, as a means for delivering to the enemy, sometimes overtly, sometimes in stealth, a considerable destructive threat. Although a IXC like U—515 carried two deck guns on its upper casing, a 10.5 cm forward and a 3.7 cm aft, as well as one or two 20mm anti-aircraft guns on a platform aft of the conning tower, and although some boats (notably the IXB U-123) had sunk shipping with gunfire alone, the World War II U-boat’s main armament was always the torpedo. A IXC could carry as many as twenty-two torpedoes. Normal stowage on a Feindfahrt (operational patrol) was fifteen to seventeen. These cigar-shaped weapons would be stored as action-ready in the launch tubes, of which the IXC had six, four bow and two stern, and as reserves under and over floor plates or in chains or cradles that temporarily displaced sleeping bunks in the fore and aft torpedo rooms.

Additional stowage was provided by six containers under wood slats between the pressure hull and the upper deck casing, but by 1943 U-boats rarely used them because of the length of time it required the crew to winch a torpedo down the open forward hatch, a period during which the boat was critically vulnerable. Concern was spreading by April 1943 that the Allies possessed new, more powerful depth charges, as evidenced by increased cases of damage to the upper deck containers. Should those containers fracture and fill with water, and should weight thereby suddenly increase to offset the trim, a submerged U-boat could fall fatally out of control. For this reason, as well as for the fact that the now constant danger of air attack had deterred boats from reloading at sea, BdU ordered all boats of whatever type preparing to sortie from base to leave their containers behind.

Technically speaking, the action-ready torpedo in a tube was not “fired” during combat, for no explosive powder was ignited to serve as a propellant. Rather, the tube was flooded and the torpedo was “launched,” or “released,” by a blast of compressed air at about twenty-four atmospheres of pressure. The usual command was Los! (“Release!”) (It should be noted, however, that the word shot [Schuß] was frequently used in U-boat KTBs to indicate a torpedo launch, and the report of a launch filled out by Watch Officers was called a “Shooting Report” [.Schussmeldung].) Once released, the torpedo became an independent, self-propelled submarine of its own, with guidance system, engine or motor, propellers, rudders, and hydroplanes, which steered its high explosive warhead to immolation against or under the hull of an enemy ship. Its destiny was to tear a hole in that hull, causing the ship to sink. U-boat men called their torpedo an Aal (eel). Henke’s U-515 carried two types of eels:

T-I, G7a, “Ato”: This torpedo, standard armament throughout the war and valued for its dependability, was driven by a gassy steam generated by a combustion of alcohol and compressed air. Power was passed through a turbine to a single six-bladed propeller. Speed settings permitted runs of 30, 40, or 44 knots for ranges, respectively, of 12.5 kilometers, 7.5 km, and 6 km at depths below the surface prescribed by the launch officer. In daylight, the G7a left a visible surface wake of exhaust gases (bubbles). The warhead, filled with 280 kilograms of high explosive, was detonated by a Pi 3 pistol that was activated either by impact on a ship’s hull or by magnetic influence of a ship’s keel. The Pi 3-equipped G7a. had a tendency to explode at the end of a miss run. The “G” stood for type number; the “7” for length, 7.16 m (7.8 yards); the “a” for air-steam propulsion. Diameter of the G7a was 53.46 cm (21 inches), the same as for the British Whitehead torpedo.

T-III, G7e, “Eto”: This type was propelled by a 100 horsepower electric motor powered by lead-acid wet cell batteries that drove a pair of two-bladed counter-rotating propellers. An improved model of an earlier electric eel (T-II), the T-III, or G7e, was the more common weapon on board U-boats in spring 1943. It had all the same dimensions as the G7a and the same warhead weight. A Pi 2 pistol allowed for both contact and magnetic detonation. The latter was the preferred setting, since, instead of releasing most of its energy upward alongside the hull in a detonation plume, it directed its major force directly upward against the keel, theoretically sinking the target with a single explosion; but see U-515’s two coups de grace with California Star. The T-III’s principal advantage was that it left no bubble wake to give away the U-boat’s position. Its main disadvantages were: (1) it was slow (30 knots only) with a short range (5 km), and that only if the batteries were pre-heated to 30°C before launch; and (2) the G7e—the “e” standing for electric—had to be serviced every three to five days in order to maintain its complex innards, particularly the power system.


The U-515 was not yet equipped with the newest operational torpedo type, FAT, for Federapparattorpedo (spring-operated torpedo). This weapon, also called the Geleitzugtorpedo (convoy torpedo) was a G7a (“Atofat”) or G7e (“Etofat”) fitted with a guidance system that caused it to take a direct course for a given range toward a convoy’s ship columns, then to turn right or left and describe a succession of long or short legs, or loops, the expectation being that a snaking, to-and-fro course through the columns would result in a random Treffer, or hit. FATs, which the British called “Curlies,” were still not common equipment in spring 1943. The U-515 would not receive FATs until her fourth cruise, beginning 29 August, when she would also carry another new torpedo type, introduced the previous February and March, the acoustic anti-escort T-V, G7es, called Zaunkönig (wren), which was designed to home in on the cavitation noise (24.5 kHz) of an escort vessel’s propellers running at 10 to 18 knots. This type, which was even rarer than the FAT on U-boats at sea in spring 1943, would have its first success in combat in September.

Most of the officers and crew who launched U-515’s eels had served together since the boat was commissioned. In that respect they were unlike the typical crew, some of whose enlisted members normally transferred out of a boat following two patrols in order to take the classwork and training required to qualify them for a new specialty, higher grade, or both, after which they would be assigned to different boats. Somehow, Kptlt. Henke had avoided that rotation, with the result that he commanded an unusually high number of experienced twenty-two-year-olds at a time when the average age of non-petty officer crewmen was a year or two younger. Furthermore, at the date of commissioning, Henke had inherited a cadre of petty officers (23 years old and older) who had had prior experience on Type IX boats.

This veteran crew, most of them U-boat volunteers, was motivated, we may believe, not only by the usual inducements of proud service in an elite arm; education in the latest technology, specially high pay rates, including combat patrol bonuses; the best rations to be found in any of the German services; generous leaves; and the near-certainty of medals, including Iron Crosses first and second class; they were also motivated by the success of their Commander in sinking ships, for that was the particularly energizing tonic on a U-boat. Many negative distractions could be set aside, for example, lack of promotion opportunities because of the crew’s continuity of service on this particular boat, Henke’s sometimes severe disciplinary responses to minor crew infractions, or the festering personality conflict between the Chief Engineer and his senior engine room machinist—all of that mattered little if the boat was going from success to success with her torpedoes. When, at last, U-515 succumbed to U.S. Navy destroyers on 9 April 1944, American interrogations of her survivors disclosed that even at that date, when the Atlantic war was long before lost, morale aboard U-515 remained high.

The thirty-three-year-old man who commanded Fünffünfzehn (515) was one of the most enigmatic and troubled Commanders in the U-Bootwaffe. Hardly the one-dimensional German type, he was an amalgam of conflicting traits. On the one hand impetuous, even hotheaded, in his performance of duty he was the model of professional cool. Uncomfortable under naval discipline himself, he was quick and rigorous in imposing it on others. Outgoing and gregarious by nature, he was viewed by his fellow officers as a vainglorious loner. Respectful of the Nazi state, which, among other things, punished Germans who listened to American popular music, he loved jazz and kept an impressive collection of Cole Porter songs on phonograph records. In stature he was five feet nine inches in height, 175 pounds. Good-looking, blueeyed, he was always the impeccably attired schöner Henke—“Handsome Henke.”

Disciplinary problems dogged the young officer during a career which, from his entrance into the Navy as an officer cadet in 1934 up to the outbreak of war, was spent mainly on shore assignments, except for two tours amounting to fourteen months on the pocket battleship Admiral Scheer. In March 1940, he was ordered to the U-Boat School (U-Schule) at Pillau, East Prussia (now Baltiysk, Russia). Pausing in transit at Berlin to visit a girlfriend, Henke ended up late on arrival— Absent Without Leave—by two days. Though the AWOL charge resulted from a misunderstanding of his due date, he was court-martialed and sent to duty with a punishment company. Finally allowed to complete his studies, he was assigned in November 1940 as a Second Watch Officer (Zweiter Wachoffizier, or II.W.O.) to the Type IXB U-124, based at the newly occupied port of Lorient on the Brittany coast of France. It was there that he learned that because of his spotty disciplinary record, he had lost all seniority and would have to rebuild his career from the bottom.

In four patrols on U-124, during which he advanced to First Watch Officer (I.W.O.), Henke not only redeemed his reputation but proved himself an excellent candidate for Commander’s School at Danzig (now Gdansk, Poland), to which he was assigned in November 1941. Following two months of intensive instruction in command responsibilities, simulated attack procedures, and the newest torpedo technology, Henke reported to the Deutsche Werft yards in Hamburg-Finkenwerder to assemble his crew and take command of U—575. The successes achieved during his first two command patrols with the new IXC earned him restoration of his seniority on the career list, promotion to Kapitänleutnant (Lieutenant), and the award of Germany’s highest decoration, Knight’s Cross of the Iron Cross. He was the seventieth U-boat officer to win the coveted Ritterkreuz.

Henke, his crew, his boat, and his torpedoes were fully primed for the steamy equatorial night of 30 April/1 May off West Africa.

On 13 April, after finding little else off Dakar besides Bamako, which he sank on the 9th, Henke steamed southeast past Portuguese Guinea (now Guinea Bissau) to take up a new position southwest of the busy port of Freetown, in Sierra Leone, which he reached on the 16th. But for nine days after that date, no ship traffic appeared either shoreward or seaward—a “sour-pickle time.” Nor did the conning tower bridge lookouts sight so much as an aircraft during that same period. Then, on the 25th, two British Royal Air Force (RAF) Short Sunderland flying boats came into view. Two days later, lookouts sighted a merchant vessel’s smoke, but another flying boat, this time a RAF PBY-5 Catalina flying boat, of American design and manufacture, forced the boat to dive and fall behind the contact. Better luck, it seemed, came in the late morning of the 28th, while U-515 was submerged to avoid possible morning air reconnaissance. The hydrophone (Gruppenhorchgerät, or GHG), which was an underwater passive sound detection device, picked up the sound of explosions from two series of depth charges, as well as the swish-swish-swish of warship propellers. Henke came to periscope depth and made an observation of one “London” type cruiser, four destroyers, and two passenger ships, which he assumed were filled with troops, steaming on a course of 340° (toward the northwest) at 12 knots.

Since it was daylight, he decided to make a submerged attack. The range was 5,000 meters. That would be a stretch for his Eto wakeless eels, but Henke ordered a double fan-launch (2er Fächer) from forward Tubes I and IV, with depths set to 3 and 5 meters. Both eels missed and, after eight minutes, detonated at the ends of their runs. The sourpickle time continued. And, on the 29th, U-515 had the unpleasant experience of being surprised by an RAF Catalina that dived on the boat out of dark cloud cover. The 20mm anti-aircraft gun abaft U-515’s tower gave a good account of itself with about ten hits on the Catalina, which, thrown off its stride, dropped five depth bombs harmlessly astern. After which—ALAARMM!—the boat dived, as it would have to do twice more that evening when probing Catalinas came again.

Daytime on the 30th passed uneventfully. The morning was spent submerged. Crew members who were not asleep went about their usual duties, tending to the Eto mechanisms, checking the battery arrays for chlorine gas buildup, monitoring the wireless telegraph (W/T) receivers and hydrophone, oiling the rocker-arm hinges on the nine cylinder MAN diesels, filling out report forms, studying for qualifying exams, cooking the midday meal, or shaving—Henke was one of the few commanders who forbade beards. No man wore more than shorts because the tropical temperature inside the boat exceeded 100 degrees Fahrenheit.

At 1345 German Summer Time (GST), which all boats observed no matter what their position at sea, and which was two hours ahead of Greenwich Mean Time (GMT), U—515 blew tanks and surfaced to air out the noxious and foul-smelling interior. The lookouts searched the ocean’s edge for smoke plumes, but there were none. After fifteen minutes, the boat resumed an underwater listening station, until 2041, when Henke ordered the boat surfaced again so that he and the bridge watch could survey the horizon in the day’s last light. Twenty-one minutes later, a lookout seized like a bird dog and exclaimed, “Herr Kaleu!” the diminutive of Henke’s rank. Following the lookout’s point, Henke drew into the lenses of his Carl Zeiss 7 x 50 binoculars the murky images of smoke clouds where the ocean met the sky shoreward to the southeast. He estimated the smoke at range 15 nautical miles, bearing 145°. Gradually, the images sharpened and mast tops became visible, then funnels and bridge screens. Henke counted fourteen large, fully laden merchant ships in convoy, average tonnage 6,000–7,000 GRT, proceeding northwest, guarded by what appeared to be three destroyers and five other escort vessels. Actually, the convoy, designated TS.37, was composed of eighteen merchant vessels protected by only three escorts, the smallest in the Royal Navy’s inventory: the corvette H.M.S. Bellwort and two trawlers. The convoy’s five columns had originally included a nineteenth merchant ship, but two days before she had left the formation to proceed independently, accompanied by a third trawler.

Destined for Freetown, the convoy had originated on 26 April a short distance to the east-southeast, at Takoradi, on the Gold Coast (today’s Ghana). The run between those two ports had been made many times without losses: only eight ships sunk out of 743 sailing since September 1941. It was hoped by the British Admiralty’s Flag Officer Commanding West Africa, headquartered at Freetown, that RAF overflights along the route would be a sufficient supplement to the small Royal Navy (hereafter RN) surface escort to deter U-boat attacks. The aircraft available for that purpose were one Hudson (an American Lockheed passenger plane converted to bomber) squadron and two Sunderland flying boat squadrons operating from Bathurst (Banjul, Gambia), one Catalina squadron at Freetown, and a half-squadron of Wellington bombers at Takoradi, with detachments of Hudsons at Port-Étienne (Nouâdhibou, Mauritania) and Lagos, Nigeria.

There were two sea/air escort failures, however. An interception of a W/T (radio) transmission in Morse code from Henke’s boat was made by the Senior Officer, Escort, but that fact (not the message itself, which was unknown because it was encrypted) was not forwarded or relayed directly to Headquarters, Flag Officer, with the result that three destroyers at Freetown that might have been sent out at once to reinforce the escort did not sortie until it was too late. Furthermore, at 1820 GST (1620 GMT), which was two hours and fifty-one minutes before civil twilight in the area, the one aircraft assigned to dusk patrol over TS.37 ran into line squalls and electrical storms that forced it to leave the argosy and return to base. The continuing bad weather, combined with an absence of moonlight, caused the RAF to scratch a planned all-night escort. As a consequence, by nightfall Convoy TS.37 was near-naked to its enemy.

The night was black with flashing sheet lightning across the horizons. The sky was overcast with heavy rain squalls, but visibility was good. There was a moderate sea with swell and a light westerly wind, force 3–4 on the Beaufort scale. As Henke advanced to his work, a radar detection device on board (Funkmessbeobachter [FuMB], or “Metox,” after the name of the first French firm, based in Paris, to manufacture the equipment) sounded a high-pitched alert tone through the U-boat’s loudspeaker system. Metric radar pulses from one or more surface escorts not yet equipped with 10-centimeter radar (which was outside the FuMB’s frequency range) were searching for an enemy signature. Henke continued his advance regardless and, after two hours and fifty-four minutes, still on the surface, passed under the cover of a rain squall into the rear of the convoy columns.

When he had proceeded forward as far as the convoy center without having been sighted, and there took up a position, at steerageway (the minimum speed required for helm to have effect), canted northeast across the convoy’s base course, his First Watch Officer (I.W.O.) Oblt.z.S. Ernst Sauerberg brought up to the conning tower bridge the UZO (U-boot-Zieloptik), target-aiming binoculars with fourteen-inch barrels, and attached them to the rotating UZO post bracket. With these 7 X 50 lenses, reticle-etched for degrees of elevation and deflection, the I.W.O. obtained bearing, range, and angle-on-the-bow for a Mehrfach, or multiple launch, against two target ships in one of the port columns astern and transmitted the data to the Siemens-made deflection calculator (Vorhaltrechner) manned by the Second Watch Officer (II.W.O.), Leutnant Heinrich Niemeyer, in the tower below. Meanwhile, the aft torpedo room crew opened the exterior caps of Tubes V and VI, to flood them for launch.

When the aim-off heading had been established by the calculator and transmitted to the guidance systems of the two stern torpedoes, and a depth of five meters, as decided by the I.W.O., had been hand-cranked into the eels by the torpedo room crew, Henke gave permission to launch. At 2256 GST the I.W.O. shouted Los! and hit the electromechanical launch button. PISSSHH! PISSSHH! Blasts of compressed air 1.2 seconds apart sent the two eels seaward and, 0.4 seconds after launch, the warheads activated and rudder vanes, directed by inboard gyro compasses, began to steer the warheads toward their targets. Simultaneously, Henke began counting the seconds from launch on his stopwatch; the aft torpedo room ratings vented the excess air inboard to prevent exterior surface bubbles; in the Control Room (Zentrale) the Chief Engineering Officer (Leitender Ingenieur, or L.I.) began taking water into the stern regulator tanks to compensate for the lost weight on board of the two eels; the sound man reported the torpedo runs as hot, straight, and normal; and the I.W.O. began setting up aiming triangles for four target ships forward in the convoy’s starboard columns. Henke’s war diary records:

First shot (Schuß) at 2256 from Tube V at a 6,000 GRT freighter, bows left bearing 70°. After a running time of 58 seconds, the torpedo hit amidships causing the ship to sink immediately.

Second shot at 2256 from Tube VI at a 7,000 GRT tanker, bows left bearing 6o°. After a running time of 59 seconds, the torpedo hit abaft the bridge, breaking the ship apart. The crew sent up white rockets and went quickly into lifeboats. We observed the sinking.

One minute after the first launches, the I.W.O. and deflection calculator had a trigonometric solution for a torpedo in the bow tubes. Again, Henke’s KTB:

Third shot at 2257 from Tube I at a 6,000 GRT freighter, bows left bearing 80°. After a running time of 51 seconds, the torpedo hit amidships and the vessel sank quickly.

Within the next four minutes, the I.W.O. would have aiming triangles for three more ships:

Fourth shot at 2258 from Tube IV at a 7,000 GRT freighter, bows left bearing 8o°. After a running time of 52 seconds, the torpedo hit amidships and the vessel burst apart.

Fifth shot at 2259 from Tube II at a 5,000 GRT freighter. After a running time of 60 seconds, the torpedo hit amidships and the vessel sank immediately.

Sixth shot at 2301 from Tube III at a 6,000 GRT freighter. After a running time of about 90 seconds we heard a [magnetic exploder] hit at 10 meters depth, and we thoroughly believe the ship sank.

White rockets signaling Hit By Torpedo went up in the dark night, to be joined by brilliant starshell illuminants fired by the convoy’s tiny escort in an attempt to sight the surfaced U-boat. In the same light Henke’s lookouts descried a small patrol vessel and a “destroyer” to port, and then, to starboard, another “destroyer” coming at them bows-on! Henke ordered an Alarm dive to 170 meters (562 feet). Depth charges dropped by what must have been the corvette Bellwort exploded a fair distance away. In the U-boat’s sound room the hydrophone operator heard the noises made by bursting bulkheads in the sinking ships. The torpedo crews reloaded three Etos.

Henke erred in stating that he had scored six hits and had observed five sinkings. Both his stern shots missed, despite his observations. But the rapid fusillade from his boat did result in four starboard column ships being hit, all of which would sink. First to take a torpedo was the motor ship Kota Tjandi, a 7,295 GRT Dutch vessel in British service sailing from Haifa, Table Bay, and Takoradi for Freetown and the United Kingdom. Hit on the port side, as were the three victims to follow, this ship carried 7,453 tons of general cargo, including potash, rubber waste, and 1,000 tons of tea. Of her crew of 91 plus eight Navy and Army gunners, six men were lost.

The second vessel, struck on the starboard hand of Kota Tjandi, was the British freighter Nagina, 6,551 GRT, carrying a general cargo of 4,886 tons that included 2,750 tons of pig iron. Her crew numbered 103, including eight Navy and two Army gunners. Next hit was the British steamer Bandar Shahpour, 5,236 GRT, sailing from Abadan, Mormugao, and Takoradi for Freetown and the U.K., with 6,768 tons of general cargo, including 3,000 tons of manganese ore, together with oil seeds, rubber, copra, and 2,002 bags of mail. Her crew, with four Navy and four Army gunners, numbered 62. She carried eight passengers: two women, one child, and five Merchant Navy officers. The last victim was the British motor ship Corabella, 5,681 GRT, with a cargo of 8,035 tons of manganese ore. The crew, including six Navy and two Army gunners, who, like the gunners on the other torpedoed vessels, never got a shot off at their attacker, numbered forty-eight. The four ships were all hit within six and a half minutes, and all in or near the position 07°15’N, 13°49’W.

From the Masters of Nagina, Bandar Shahpour, and Corabella we learn what happened to the crews on board those three vessels (there being no report found from the Master or crew of Kota Tjandi). Captain W. Bird stated that Nagina sighted a single torpedo approaching the ship from abeam on the port side. Its warhead exploded loudly but without a flash between Nos. 1 and 2 holds in the vicinity of the ‘tween decks and threw up a large column of water that, when it fell, crushed the fore part of the bridge. The No. 2 lifeboat and a raft were destroyed by the blast, but little other damage could be seen in the very dark night. Immediately, the ship listed about 10° to port and Captain Bird ordered engines stopped. Three minutes after the explosion, when the list increased, Bird ordered Abandon Ship. The five running lifeboats were lowered, one of which capsized. Three rafts were also launched, Bird joining the last of them.

Everyone was clear of the ship within seven minutes of being torpedoed, and from their boats and rafts they watched the holed Nagina go down, bow first, at 2113 GMT. Bird’s raft, with ten aboard, was overloaded, with the result that when three other men in the water grabbed hold of its sides, the raft capsized. The survivors managed to get purchase on the raft again, and a quarter-hour later, No. 6 lifeboat rowed over and took the thirteen on board. At 2230, H.M. Trawler Birdlip, part of the convoy escort, rescued the occupants of that boat and those of No. 5 boat. Five more survivors were found by a destroyer from Freetown but not until 3 May, and No. 3 boat with its survivors was not found, by an aircraft and a motor launch, until 4 May. Notwithstanding the exposure suffered by these last two groups, casualties were light: the Second Wireless Operator was killed by the explosion and a Chinese carpenter was missing. To Admiralty authorities, Captain Bird complained: “I do not consider that this convoy was sufficiently protected. There were three destroyers lying in Freetown Harbour; the Naval authorities must have known that this convoy was passing through this dangerous area where submarines were known to be operating, yet these destroyers were not sent to our assistance.”

Captain W. A. Chappell reported that the torpedo that struck his ship, S.S. Bandar Shahpour, was also sighted before it hit, by one of the gunners at his action station, but not in time to give a warning. The explosion, when it came, was dull and flashless, but it sent up a large column of water that then cascaded over the ship. Much of the 2,002 bags of mail, too, went skyward and came down like snowflakes over the deck and surrounding sea. Captain Chappell received reports that the mainmast had collapsed on the wireless room, destroying it and its equipment; that the engineers’ accommodation on the port side was destroyed; that the deck on the port side was twisted and fractured; and that the settling tanks in the engine room had burst, spewing oil and forcing the Fourth Engineer, who was on watch, to flee the engine room without stopping engines. Fortunately, because of the damage to the settling tanks, the engines gradually stopped on their own. Chappell fired white flares and transmitted an emergency message that was acknowledged by the Convoy Commodore. Then, deciding that the freighter’s condition was hopeless, he ordered Abandon Ship. Though the vessel was still slightly under way, three lifeboats sufficient to carry all the passengers and crew were successfully lowered; No. 4 boat became fouled and capsized on becoming waterborne. Chappell and the Chief Engineer, J. R. Black, were the last to leave, and, after a half-hour, all the survivors, with but one loss, were taken aboard Birdlip, making a total of 253 convoy survivors packed onto that small vessel. From the trawler’s gunwales the Bandar Shahpour party watched their ship go down at 2300 GMT.

When the trawler delivered her human cargo to Freetown at noon on 1 May, Chappell discovered that the dangers of being sunk were not all nautical. The accommodations provided his officers and his Goanese crew were appalling. The so-called Grand Hotel rooms assigned to his officers were so stinking and unhygienic, it was a wonder, he stated, that they did not all die from dysentery or typhoid; and the Sabars Hotel, which housed his native crew, was so foul that every man among them became sick. “They were simply wallowing in filth,” he reported, “and the food provided was uneatable; some were only given a piece of bread, with jam, after being without food for 36 hours.” No baths were available. It was worse, he said, than the boardinghouses in Bute Street, Cardiff.

The last to be struck by one of U-515’s six torpedoes was the British motor ship Corabella. While steaming at 8½ knots on a course 295°, she was struck in No. 2 hold on the port side. “It was not a violent explosion, just a dull thud,” her Master, Captain P. Leggett, reported. In his cabin at the time, he found it difficult to make his way to the bridge because of piles of wreckage and debris in the corridor. On finally making the bridge, he found it in a collapsed state, with jagged cement and iron everywhere. Looking out, he saw that the foretop mast and wireless aerial were down; worse, that the cabin containing the emergency wireless had been stove in, making it impossible to send out an S.O.S. There was no sign on deck that any sea water had been thrown up by the explosion (indicating that a magnetic exploder had detonated beneath the hull).

Rather quickly, the vessel listed to port and settled by the bow. Leggett ordered Abandon Ship. About twenty-five men made it off in the starboard boat, but as the starboard raft became waterborne its painter (the bowline used for tying up) carried away and the raft was lost.

There was trouble with the small port boat as well: it got hooked upside down to the davit for the accommodation ladder, and could not be forced loose. Leggett therefore shouted, “Every man for himself!” and the remaining crew, with the exception of the Third Officer, who was injured and would not be seen again, jumped over the side. Just before Leggett himself jumped, the ship shuddered, throwing him against hatch coamings, but he made it safely into the water, from which he watched his ship sink within twelve to fifteen minutes of being torpedoed. With a great amount of wreckage floating about him, Leggett was able to grab hold of a wood plank for buoyancy. He was soon joined by Gunner Stuart Carnelly, “but for whose strenuous efforts in keeping me afloat until help came, I should undoubtedly have drowned.”Help arrived after two hours in the form of Birdlip, which, with the addition of Leggett and Carnelly, had thirty more souls aboard her narrow decks. Five crewmen were rescued just before sunset on 1 May, and, about the same time, four more were sighted clinging to wreckage by an RAF aircraft, which dropped a rubber dinghy close to their position. Two of the men, Donkeyman William Kelly and the Cook, J. Brown, were badly injured. When the inflated dinghy splashed nearby, the other two men, Radio Operator Stuart Byatt and Second Steward George Newton, swam to retrieve it, and gave up their own places in the dinghy so that the injured men could rest more comfortably. Byatt and Newton took turns swimming and splashing around the dinghy to keep sharks and barracuda clear. And, thus, they passed the night of 1/2 May, until picked up the next morning and taken to Freetown. Altogether, nine crew members from Corabella, including the Cabin Boy, were dead or missing.

At 0130 GST on 1 May, Henke surfaced to search the area of his attacks. What he saw in the lightning-lit night was sea wrack and deck debris stretching across the swells east to west, numerous lifeboats and rafts showing lights, and then a large Bewacher (the trawler Birdlip) picking up survivors. Unaccountably, because it was not U-Bootwaffe practice to target survivors, Henke attacked the rescue vessel; exactly how, he did not say in his KTB. Also unaccountably, he failed to sink her, though she was probably stationary in the water. Documents presented after the war to the International Military Tribunal at Nürnberg disclosed that Hitler had several times insisted that U-boats should kill survivors by shooting up their lifeboats, as a means both of denying those crews to new ships and of intimidating other crews from going to sea.

No formal order to that effect was ever traced to Admiral Dönitz, although, where “rescue ships” were concerned, in autumn of 1942 he had stated in an order: “In view of the desired annihilation of ships’ crews their [rescue ships’] sinking is of great value.” Apparently, to sink a warship containing survivors was understood by Dönitz to be of a different moral character from the sinking of survivors in a lifeboat. Not exactly a directive to do so, his ambiguously worded order could nonetheless be interpreted by a Commander as permission to sink a rescue vessel, if the opportunity presented itself, and that may have guided Henke with respect to Birdlip. On balance, Dönitz seems to have resisted Hitler’s pressure to engage in Schrecklichkeit (terribleness, dreadfulness), on the grounds that it violated international conventions governing sea warfare, that it compromised the honor and integrity of the U-Bootwaffe, and, more practically, as the German Naval Staff expressed it on 16 December 1942, that: “The killing of survivors in lifeboats is inadmissible, not just on humanitarian grounds but also because the morale of our own men would suffer should they consider the same fate as likely for themselves.”

At Nürnberg the only documented incident of incorrect behavior toward survivors presented by the Allied prosecutors was a machine gun attack on the merchant crew of S.S. Peleus, a Greek vessel, in the Indian Ocean on 13 March 1944. The boat responsible was U-852, commanded by Kptlt. Heinz Eck. Captured after the war and placed on trial together with his officers by a British court-martial, Eck denied that he had received any orders, directly or ambiguously, from Dönitz to shoot at shipwrecked survivors. The Commander, his I.W.O., and the ship’s doctor, both of whom had joined in the shooting, were executed by firing squad on 30 November 1941.29

In the main, existing records support the contention that German U-boat conduct toward survivors was correct, even on many occasions solicitous when crews provided them food, water, medical supplies, compasses, position, and course to land. Werner Henke’s biographer describes his subject as similarly “humane,” though in the particular case at hand Henke may be said to have backed into the compliment by his failure to destroy the rescue vessel Birdlip and her human cargo.31That incident closed, and with three new Etos in the bow tubes, Henke called for A.K. voraus—“Both ahead full!” He would pursue the convoy north and see what damage he could do to its remaining ships. At 0513 he sighted its trailing edges, and twenty-seven minutes later, with the air still very dark and visibility down to medium, he nosed his way into the convoy columns, as before, from astern. First Watch Officer Sauerberg took a reading on three separate ships to port that were steaming, he estimated, at 7 knots. Three Etos in the bow tubes were set to run at 7 meters depth, Pi 2 pistols fixed for magnetic detonation. Henke’s KTB:

First shot from Tube IV at a 6,000 GRT freighter, bows right bearing 100°. After a running time of 68 seconds the torpedo hit below the aft mast causing a very wide detonation column containing ship fragments. The steamer burned. We assume it sank.

Second shot from Tube I at a 6,000 GRT freighter, bows right bearing 90°. After a running time of 65 seconds, this ship, too, put out a wide detonation column. It burned immediately. We assume it sank.Third shot from Tube III at a 7,000 GRT freighter, bows right bearing 90°. After a running time of 35 seconds, the torpedo hit toward the stern causing a large detonation and flames that shot very high. Apparently, artillery ammunition went up. We observed the burning stern sink.

By 0549 the sky was alive with starshells and white rockets that illuminated two nearby “destroyers.” There were three RN destroyers that had come on the scene belatedly from Freetown: H.M.S. Rapid, HMS Malcolm, and HMS Wolverine. Henke crash-dived in the shallow (80 meters, 250 feet) coastal water, seeking temperature gradients and varying density layers that abounded there as a protection against the inevitable British sonar detection pulses (called asdic). Taking a southwesterly course toward deeper water, U-515 again succeeded in eluding her pursuers. The sounds of depth charges and of ship hulls fracturing receded astern.


Henke’s rampage was over. And this time his observations were all correct. During one remarkable night he had equaled the record seven sinkings [plus one damaged] in a single twenty-four-hour day achieved by U-boat “ace” Kptlt. Joachim Schepke (U-100) against Convoy SC.II on 23 November 1940. And he had exceeded the earlier best night of six sinkings (one damaged) posted by Kptlt. Otto Kretschmer (U-99), the “tonnage king,” on the night of 18/19 October 1940, one of three nights (17–19 October) during which nine U-boats savaged Convoys SC.7 and HX.79 off Rockall Bank near Ireland—nights that came collectively to be called in Germany die Nacht der langen Messer, “The Night of the Long Knives.”33 (This phrase, earlier used to describe Hitler’s bloody purge of Ernst Rohm and his SA [“storm troopers”] leadership in 1934, originated in a medieval legend, known in both Germany and Britain, that told how Saxons who invited the British king Vortigern and his leaders to a banquet slaughtered three hundred of the leaders with their long knives.)

There was no glory for the merchant seamen, of course. Though their cost in lives was less in Henke’s second fusillade, the newly afflicted seamen of Convoy TS.37 experienced anyone’s full share of “peril on the sea,” which, it must be added, they managed with commendable composure. First hit this time was the Belgian freighter Mokambo, 4,996 GRT, out of Matadi and Takoradi for Freetown and the United Kingdom with a cargo of 1,139 tons of palm oil, 1,520 tons of kernels, 440 tons of copal, 2,000 tons of cotton, 2,000 tons of copper, and 38 tons of wolframite. Other than that the weather at the time was cloudy and showery, that the sky was still very dark, and that there was a slight sea with a west wind, Force 3 on the Beaufort scale, there are no surviving details of her sinking.

Henke’s second victim was the British steamer City of Singapore, 6,555 GRT, which was sailing from Calcutta and Takoradi for Freetown and Liverpool. Her cargo was 9,000 tons, which included 2,750 tons of pig iron, 2,750 tons of general cargo and mail, and, the remainder, jute, linseed, and groundnuts. The ship was hit by a torpedo that exploded just abaft the mainmast on the starboard side, throwing up a tall column of water but showing no flash. The hatches and beams from No. 5 hold were crushed; No. 4 hold flooded; the deck gun was blasted off its platform onto the deck; one of the six lifeboats was rendered useless; and the remaining boats, like the ship as a whole, were completely covered with oil from the tanks.The Master, Captain A. G. Freeman, followed the book: He stopped engines; sent out wireless messages, which were acknowledged; fired two white rockets and showed the red light; and, when the ship had almost lost headway so that boats could be lowered without fear of their capsizing, he threw the Confidential Books overboard and ordered Abandon Ship. Freeman left last in No. 2 boat after making certain that no one remained on board. By that time, the ship was quickly sinking aft and the poop was awash. Fourteen minutes after the torpedo hit, Freeman heard a loud report, which he assumed was the No. 4 deep tank bulkhead collapsing, following which the vessel folded in two and disappeared. An hour and a half later, the survivors were picked up by Birdlip and by the convoy’s second trawler, H.M.T. Arran, and taken by them to Freetown. Not one of the eighty-seven-man crew and two gunners had been lost. Freeman reported: “I consider this Convoy was inadequately escorted.”

The last ship to be hit by Henke, who had expended only nine eels to cause seven sinkings—an unusually successful economy of firepower—was the British freighter Clan Macpherson, 6,940 GRT, out of Calcutta, Durban, and Takoradi for Freetown and the United Kingdom with 8,421 tons of general cargo that included 2,750 tons of pig iron, plus zinc, mica, jute, linseed, tea, and groundnuts. His crew, including gunners, numbered a large 140. No one saw the track of the torpedo, which exploded, “not violently,” in No. 2 hold on the starboard side. Knowing that the hold was 100 feet in length and 134,000 cubic feet of space, and fearing that it would fill quickly, the ship’s Master, Captain E. Gough, immediately ordered Abandon Ship. He switched on the red light, fired two white rockets, sent out a W/T message, and threw overboard the Confidential Books.

“All my men lined up like soldiers,” Gough reported, “no one attempted to do anything without orders, and within ten minutes the five lifeboats and the one small boat were clear of the ship,” which, they saw, did not go down as expected. The men on the small No. 2 bridgeboat were taken on board a freighter, Silver Ash, and the occupants of the other five boats, keeping in contact with each other by means of flashlights, had the opportunity of being rescued by Arran; but, instead, Gough asked the trawler to stand by them until daybreak, when he and the crew from the five boats reboarded their still floating vessel. The pumps were put on and all the engineers went below to raise steam. By 0920 the ship was under way doing twenty revolutions, and Gough had her under helm on a course of 047° toward Freetown, some 67 nautical miles distant. But, after a short while, it became apparent that No. 1 hold was filling, and some measure had to be taken to balance the ship.

Accordingly, Gough ordered the Chief Engineer in the engine room to fill tanks Nos. 4 and 5 in an attempt to bring the boat down by the stern. When that action was completed, though, the ship was listing to starboard, and the sea was lapping at the fore deck. Gough rang the engine room: “Finish With Engines.” He thought he might take a tow, stern first, from Arran. But it was no use. Clan Macpherson was not going to make it. He again ordered Abandon Ship and personally phoned the engineers and engine room crew to order them out. Unfortunately, two minutes after the boats were away, the ship suddenly upended, hung there in that state, quivering, then sank in a frothy gulp, and there was no sign in the boats of Chief Engineer Neil Robertson, or of the Second, Fourth, and Fifth Engineers, “who were just a little slow in leaving the engine room.”

In his report Gough complimented a half-dozen Lascars (East Indians) in his crew who had gone into No. 1 hold and, working up to their waists in water, tried to build up a bulkhead with bags; had the bulkhead collapsed, “all would have most certainly been drowned.” The boarding party reached Freetown Harbour at 2015 GMT on 1 May, where the Europeans, including Masters and Officers, were assigned to the ghastly Grand Hotel and the native crew were placed in even grimmer boardinghouses. By 10 June, so far as Gough knew, the natives were still housed in squalid conditions, with awful food, if any, and no water for bathing, most of them afflicted with boils and diarrhea. The extent of the suffering caused by U-boat warfare was simply unknown to its perpetrators.

In London, Prime Minister Winston Churchill called the heavy sinkings “deplorable.” His Anti-U-Boat Warfare Committee invited an explanation for the lack of air cover provided Convoy TS.37 from Sir Archibald Sinclair, Bt., M.P., Secretary of State for Air. Sinclair responded that, “Bad weather was responsible for the absence of air escort during the night on which the 7 ships had been sunk.”

Inside U-515, as the opening day of May drew to a close, Werner Henke received a Funkspruch (wireless signal) from BdU in Berlin acknowledging his report of the sinkings. It consisted of one word: BRAVO. Henke recorded his and the crew’s reaction to it: Große Freude im Boot—“Great elation in the boat"

On the same 1 May, U-659, commanded by Kptlt. Hans Stock, was patrolling 380 nautical miles west-northwest of Cape Finisterre (“land’s end”), the rocky promontory at the most westerly point of Spain. A Type VIIC, U-659 was one of eleven boats that had been formed by BdU into Gruppe Drossel (Group Thrush).44 Stock’s orders called for him eventually to break through the Strait of Gibraltar into the Mediterranean, but his first duty since the boat slipped her moorings at Brest on Easter Sunday, 25 April, was to form part of the Drossel disposition in a controlled operation against Allied coastwise traffic on the U.K.-Gibraltar-West Africa run. At night on 1/2 May the Drossel boats were advised by BdU that a British cruiser-minelayer, H.M.S. Adventure, was somewhere in their neighborhood. Stock decided against pursuing the faster vessel.

No smoke plumes appeared on the second day, but early on 3 May, following her regular forenoon exercise dive to correct trim, U-659 received an F.T. (Funktelegraphie, wireless message) that a reconnaissance Focke-Wulf 200 Kondor aircraft of Fliegerführer Atlantik based in western France had sighted a southbound convoy of eleven cargo ships and six escorts in position approximately 44°N, 14°W. Stock moved eastward at full (flank) speed (äußerste Kraft) to the attack. About 1400 GST, he learned from BdU of the presence of a second southbound formation, consisting of twenty-seven vessels, in nearly the same position as the first. Stock decided to go after the second set of targets instead. Before midnight, as the sea state was deteriorating, he ordered another dive to adjust trim.

“Clear the bridge!” The dive order sent the bridge watch scrambling down the conning tower hatch. The Watch Officer, last man through, pulled the hatch closed and wheeled the spindle home in its bed. Meanwhile, in the Zentrale (control room) below, the Chief Engineering Officer (L.I.) had ordered, “Vent main ballast!” and slammed the ball of his hand against the dive bell, which shrilled throughout the boat. At once, two dozen pairs of hands in the control room and aft in the engine and maneuvering rooms whirred among banks of red and black valve wheels, overhead vent levers, and panel switches to open the external ballast tanks to water, cut off the outside air intakes and exhaust valves for the diesel engines, and engage the E-motors for underwater running.

Stock probably instructed the L.I. to level off at periscope depth, while he himself checked a stopwatch against both the column of mercury in the periscope elevation indicator and the needle on the Tiefenmesser, or depth manometer, expecting to see thirteen meters of water put above the hull inside thirty seconds. Facing the hull on the starboard side, two planesmen operated brass buttons, up and down, that controlled protruding bow and stern hydroplanes, which, like an aircraft’s horizontal stabilizers, caused the submerging U-boat to pitch at a certain angle. Soon, with the diesels’ roar and vibrations stilled, only a faint hum heard from the E-motors aft, and every crew member silent at his diving station, the sea closed over U—659.

The senior planesman reported when the mercury column showed 13.5 meters, periscope depth, and the L.I. ordered the planes brought to neutral and jockeyed to maintain as much as possible a constant level attitude while he went about the critical business of adjusting the boat’s weight and tilting movement. This he did by pumping water by the hundreds of kilograms fore or aft between trim tanks at the extreme bow and stern. Maintaining trim was crucial, lest in an emergency dive the boat either plunge to the seabed or broach the surface, bow-or stern-first. Meanwhile, the Helmsman (Rudergänger), stationed on the forward starboard side bulkhead, steered the boat by compass, using brass rudder buttons for “port” and “starboard,” and the Navigator (Obersteuermann) at his high table plotted the boat’s position.

Just forward of the amidships control room, and reached through a watertight circular hatch offset to port, were the Commander’s felt-curtained bunk and desk space on the port side of a narrow fore-and-aft gangway, and, on the starboard side opposite, the wireless (Funkraum) and hydrophone (Horchraum) rooms. Continuing forward, one came upon the bunk-long accommodation of the I.W.O., II.W.O., and L.I. (Offizierraum), where a mess and worktable along the port side enabled this compartment to serve as a wardroom. Beyond, through another hatch, was bunk space for four men of Chief Petty Officer rank (Oberfeldwebel), though U-659 carried only three, and, farther still, past a portside head, one reached the forward torpedo room (Bugtorpedoraum), home not only to the four bow torpedo tubes but also to the majority of the ratings, popularly called “Lords” (Pairs).

Here the hull narrowed markedly, accentuating the cramped interior of the smaller Type VIIC boat, made all the more confined by the conditions attendant to a just-commenced Feindfahrt: two of the room’s spare torpedoes, hung by hoist rings suspended from an I-beam, displaced sleeping bunks; food crates, sacks, and cans occupied every nook and cranny of floor space; while overhead hammocks bulged low with hams, sausages, fruits, and Kommissbrot, the hard navy black bread. The only way to get about was by hands and knees. Every man yearned for early attack successes, so that the two spare “eels” in the bunk areas could be placed inside the white-painted tubes, and the lashed-up bunks, with their blue-and-white-checked gingham sheets and pillowcases, could be brought down for sleeping and sitting.

None of the Lords would be nearly as anxious, however, about getting rid of the brow-bruising fresh food hammocks. They knew that once the perishable fresh food was consumed they would have only tinned food to eat, and that by the time that exchange came to pass, every bucket of food hauled down the passageway from the galley would take on a taste compounded of the boat’s accumulated vapors of stale, humid air, diesel oil, battery gas, bilges, oven fumes, soiled trousers, unbrushed teeth, urine, vomit, semen, smegma, and Colibri cologne. By then, too, the gingham sheets and pillowcases of the “hot bunks”—so-called because they would be constantly occupied day and night by seamen and technicians coming off their various watches— would be making their own gamy contributions to the putrescent atmosphere.

Returning to the control room through the constricted steel cylinder (though not a perfect cylinder for its whole length) that was the VIIC’s pressure hull, one walked over a storage area almost as large as the working and living space above. Beneath the floor plates were lead-acid storage battery arrays whose dead weight counterbalanced the diesel engines and a second battery compartment in the after section of the boat. Here, too, was stored ammunition for the deck and anti-aircraft (flak) guns.

The rolled galvanized sheet steel skin that formed the pressure hull itself thickened as one approached the control room, from 1.6 cm at the bow and stern to 1.85 cm amidships, and to 2.2 cm where the conning tower joined the hull. Passing through the control room, which was 6.2 meters (20⅓ feet) across the beam, one came to a circular hatch that led into the Petty Officers’ accommodation (Unteroffizierraum) and, after that, the galley (Küche) with its little Vosswerke stove, short refrigerator, sink, and pantry that served the single cook (Smutje). From there the boat’s one central, single-level gangway opened to the oily and smelly, but now silent, engine room (Dieselmotorenraum), where twin MAN 6-cylinder, 4-cycle engines of 1,160 horsepower each provided surface propulsion.

The humming dynamotors were in the next compartment aft, the E-Maschinenraum, or maneuvering room. Here, by contrast to the appearance of the engine room, two clean E-Motors that sparkled beneath equally gleaming control panels drove the boat’s two propeller drive shafts underwater. There was other equipment in this room as well, including an electricity-driven air compressor on the port side and a Junkers diesel-driven compressor on the opposite side, which were used for filling containers of the compressed air that the control room required for blowing water from the ballast tanks when the boat surfaced and for launching torpedoes. Here, too, was an auxiliary steering wheel for use in moving the double rudders in the event the electrical steering buttons in the control room were disabled. From the maneuvering room it was then just a few steps into the aft torpedo room with its lone white-faced launch tube. Every three days the Eto that occupied that tube, or the one spare stowed beneath the E-motors, would be opened up and inspected by the torpedo mates, called “mixers.” Under wire-shielded lights the mixers would unscrew inspection plates and test the eel’s battery level, electric motor, guidance system, and depth-keeping mechanism.

The mixers and other crew members who occupied the interior space of U-659 were, like the crewmen of all U-boats, a selective, highly trained group. The four officers were all graduates of the Naval Academy (Marineschule) in Flensburg-Mürwik, a cadet training establishment through which the future officer passed after a year of practical experience that included three months at sea. Following the Academy curriculum, they would have spent eight to twelve weeks at U-boot-Schule in Neustadt in Schleswig-Holstein or Pillau (after 1940). Twenty-seven-year-old Stock, the Commander, had been a member of the 1935 entering class (Crew 35). After receiving his commission and completing several operational training courses, he had served as I.W.O. with Kptlt. Heinrich Lehmann-Willenbrock on U-96. (It was on the cruise of U-96 in late 1941 to the North Atlantic and Mediterranean that Lothar-Günther Buchheim, a twenty-three-year-old war correspondent who accompanied the crew, based his much later novel [1973] followed by a motion picture, both named Das Boot [“The Boat”].) After Commander’s Course with the 26th Flotilla at Pillau, Stock was given the new boat U-659, which he commissioned on 9 December 1941 and took on four patrols prior to this one.

By 1943, with most of the surface Navy frozen in port, the majority of young officers, such as Stock’s I.W.O., II.W.O., and L.I., were assigned to U-boats. By contrast, most of the boat’s petty officers and lower ratings were volunteers. Twenty to twenty-four years in age, they had entered the Kriegsmarine from hometowns situated largely in northern and central Germany: Hamburg would be an example of the former, the Ruhr and Saxony districts examples of the latter. Their formal schooling prior to trade schools did not exceed the requisite eight primary grades, and their religious affiliations were roughly three-quarters Protestant, one-quarter Roman Catholic. Some crewmen had volunteered directly from civilian life for the U-Bootwaffe; others had served previously on light surface vessels.

Generally speaking, the crewmen fell into two categories: seamen (Seemänner), which included helmsmen, planesmen, lookouts, gunners, the deck force, cook, and stewards; and the engineering/technical personnel (Techniker), who operated the boat’s seagoing and torpedo attack equipment, such as the diesels, E-motors, torpedo mechanisms, radio, hydrophone, and the diving and surfacing systems. The second category had a high representation of nonspecialized entry-level metalworkers from the industrial regions of central Germany—young men who might be expected to feel comfortable in an all-metal environment, who had a common vocational experience to bind them together as comrades, and who possessed the canny skills to contrive emergency repairs when the boat was far from base. All hands would have received three months of basic naval training, followed by three to six months of intensive course work at U-Boat School, either at Neustadt prior to May 1940, or at Pillau from May to November 1940, or at Gdynia after the latter date.

Whatever their backgrounds, categories, or ratings, the crewmen of U-659, like all U-boat men, shared certain communalities. Everyone ate the same food, used the same head (a second head aft was usually employed as a pantry for canned foods), and breathed the same foul air. Nor was there any dress code to distinguish ranks from ratings, petty officers from mates. Except for the tropical white cover worn on the Commander’s Schirmmütze, or peaked cap (for visual identification at night), every man’s attire had a dull sameness. Most wore standard blue-gray fatigues, perhaps with a Schiffchen, or forage cap, made from blue wool with black lining. In cold weather one saw sweaters knitted by grandmother and other unconventional mufti.

On the bridge in cold weather the watch officer and lookouts wore gray-green leathers, and, in heavy weather, sou’westers. When in warm waters, on the other hand, short pants of varying hues were the dress of the day. In one other particular, too, the crewmen were aware of their societal cohesion: at sea every man depended absolutely on the performance of every other. In no other war machine was the integral participation of every team member so vital. Any one man of them could sink the boat. One hatch uncovered, one valve unturned, one battery array unchecked for gas, one enemy aircraft unspotted, one vessel on collision course unsighted, and the mission, boat, and crew were doomed.

The trim secured, Stock took a careful look around the horizon and sky with the wide-angle sky periscope, whose shaft dominated the forward center space of the control room, and, seeing no enemy ship or aircraft, he ordered: “Surface!” The L.I. accordingly instructed his ballast tank operators, “Blow main ballast!,” listened approvingly as the hissing compressed air expelled water from the ballast tanks (diesel exhaust would finish the task on the surface), and called out the upward cant angles on the fore and aft planes. When the E-motors had driven the boat dynamically forward to the water’s surface and the conning tower bridge hatch had broken clear (”Turmluk ist frei, Boot ist raus!”), the diesels were lit, and Stock pounded up the aluminum ladder that ran up through a hull hatch into the tear-shaped conning tower (Turm) that housed the fixed attack periscope eyepiece, the torpedo deflection calculator, and a compass repeater with rudder buttons.

After opening the upper tower hatch, Stock stepped up onto the dripping open bridge, where he was followed by the I.W.O., commanding the midwatch, a seaman Petty Officer, and two seamen. Since the seas were heavy, with waves breaking against the tower, the boat was now pitching and rolling sharply in the riled-up water, and the men at once attached their safety harnesses to brackets extending out from the bridge’s wood-slatted enclosure. From the bridge, Stock and the lookouts could see, fore and aft, the full length of the boat’s deck casing, 67.1 meters (221⅓ feet), with its hardwood planking, and along the waterline to either side the long, bulging “saddle tanks,” which contained, among their various bunkers, the main fuel oil and ballast tanks. Under diesel propulsion the boat threw up frothy bow and stern wakes, all the more pronounced because of the shuddering dark rollers.

Movement on the bridge was constrained by the periscope shafts, the sky scope forward, the attack scope aft, and the UZO post with its bracket for the surface attack optics set above a ring marked off in compass degrees. Other equipment on the bridge included a gyrocompass, magnetic compass, engine telegraph dial, extendable radio antenna, and voice pipe. The space was enclosed front and two sides by doubleplate steel cladding that rose to a height of 1.5 meters above the bridge deck, as a protection against hard seas and small-to medium-arms fire. Aft of the bridge was a circular, railed-in flak platform for the 20mm anti-aircraft gun—and for cigarettes and pipes in calmer weather, when crewmen thought of it as a Wintergarten.

With the bridge set only seventeen feet above the water, Stock and his lookouts had limited vision of the horizon, acquiring through their 7 x 50s about twelve kilometers range in ideal visibility conditions on a clear day, and much less on a night like this night, when visibility was poor. An additional one or two kilometers might be gained by shinnying up the extended sky periscope standard. As a result of the VIIC’s low silhouette, its visual search rate was never more than 2,350 square nautical miles per day, in good conditions, as compared with the larger and faster U.S. Navy fleet submarine’s 7,000 to 10,000 square nautical miles per day: the U.S. sub had brackets built on the periscope shears (supports) that enabled it to place eyes thirty-five feet above water. But for Stock and the midwatch later this night, 3/4 May, at 0325 GST to be exact, distance vision proved not to be a factor. In the event that now unfolded it would have been better had they all been nearsighted, as—


The boat careened hard to port from a ramming amidships on the starboard side. The lookouts were startled by what they now saw: the crushed bows of another U-boat! Below, water and fuel oil poured into the control room and other compartments. The L.I. called up the voice pipe to inform Stock that the inrush of war was so great it could not be stanched, and the boat could not long be kept afloat. Stock and the I.W.O. went below, where Stock, finding the L.I. up to his chest in oil, ordered the crew to don life jackets and abandon the boat: “Alle Männer aus dem Boot!’

Men scrambled up the tower ladder, then down the tower sides, and mustered on the tossing upper deck—though not all of them, since it appears that some of the engine room personnel and radiomen remained on duty too long to make their escape, and that both Stock and the I.W.O. similarly got trapped below. Among the officers, in fact, only the L.I. made it out. Survivors stated that the radio operators got off a short signal reporting both the boat’s loss by ramming and her position, 43°32’N, 13°3o’W. Five minutes after the collision, a towering wave broke over the mortally wounded frame of U-659. The men on deck went flying into the water, and the boat, heeling over to starboard, sank from view.


The other boat was U-439, a Type VIIC commanded by Oblt.z.S. Helmut von Tippelskirch (Crew 37). A native of Cuxhaven, the twenty-five-year-old Kommandant had earlier served as I.W.O. on U—160. The U-439, his first command, had departed Brest on 27 April, and on the night of 3/4 May occupied a station adjoining U-639 in the Drossel line, from which she was proceeding this night at the highest speed that the sea state permitted, to intercept the first of the two reported southbound convoys. By 0100 GST she sighted the convoy and by 0325 she was positioned ahead of it, making seven knots. At that instant, survivors from his boat said, Tippelskirch altered course slightly to port and his bows rammed the starboard side of U-639, which no one had seen. Tippelskirch immediately ordered both engines full astern, but the maneuver in rough seas caused the diesel exhausts to drown and the interior of the boat to fill with blue fumes. Because the collision had caused heavy leakage through the two port bow torpedo tubes, the bow compartment had to be closed off.

Meanwhile, the L.I. tried to adjust the surface trim by blowing the forward ballast tanks, but these, it was discovered, had been damaged in the collision. He compensated by flooding some of the after tanks, but this brought the boat dangerously low in the water, and the L.I. recommended abandonment. Tippelskirch, thinking the boat might yet be saved, ordered the engine room personnel and radio operators to remain at their stations and the remainder of the crew to go up on deck with their life jackets. There they saw that their boat was down by the bows and already half-submerged. Survivors doubted that the radiomen’s distress signals were heard, since most of the forward transmitting antenna wire was underwater. Said one:

The Commander sent a W/T [radio] message: “Boat rammed, boat sinking, crew abandoning ship.” Messages should be ciphered if possible, so that the English shouldn’t understand; and they [the radiomen] calmly ciphered the whole message and tapped it out to the last letter, and the water had already reached their feet. The message went out. Perhaps they [BdU] received it, perhaps they didn’t.

They did not receive it

From the bridge Tippelskirch could see the other U-boat not far distant. Though it appeared to be in a sinking condition, he asked it by signal lamp for assistance; but U-659 replied by lamp that she, too, was going under. Then a huge rogue wave, probably the same that swamped Stock’s boat, drove U-439, still carrying inside about twenty-four engine machinists and radiomen, into the 2,761-fathom deep, a bourn from which none returned. Those men who had been on deck, thrown off violently from their tenuous footing, swam off with flashing signal lights, hoping to attract either other Drossel boats or, just as well given the circumstances, the enemy.

At 0500, Royal Navy Motor Torpedo Boat MTB 670, leading the starboard column of the first reported southbound operational Coastal Forces convoy, ran into diesel smoke and fumes, and afterwards sighted men swimming in the water. The starboard column stopped and rescued twelve survivors, three from the forty-five-man crew of U-639, and nine from the forty-eight-man crew of U-439. The only officer among them was the L.I. of U-639. Taken first to Gibraltar and then on 13 May to the Combined Services Detailed Interrogation Centre, U.K., at Latimer House, Chesham, Buckinghamshire, England, the survivors underwent the usual interrogation by RN officers. The nine from U—439 proved particularly intractable, and the interrogators reported, “They were mostly more security-conscious than has been the case among recent U-boat prisoners of war.” All they would say about their Commander, Tippelskirch, was that he was adventurous and very popular with his men, but that, having teethed on a Type IXC (U—/160), he always had difficulty handling a VIIC. About the I.W.O., Oblt.z.S. Gerhard Falow, they had mixed feelings: on the one hand, they found him easygoing and well-liked; on the other, they thought him lazy and personally responsible for the loss of their own boat, and of U-659 as well.

Apparently, Falow himself, before his watery death, agreed with that last judgment, as the British learned in detail from the secret bugging of twenty-one-year-old Herbert Apel, a U-439 Maschinengefreiter (the U.S. Navy equivalent: Fireman, third class; the Royal Navy: Stoker, second class). The interrogators housed Apel in a POW hut with a Steuermann named Schultz from SS Regensburg, a German blockade-running freighter that had been intercepted , shelled and sunk by the Royal Navy heavy cruiser HMS Glasgow off the north of Iceland on 30 March 1943. The interrogators knew that a man from one boat or ship would want to relate his experiences, knowledge, and thoughts to someone he did not know from another U-boat or ship.

Accordingly, on 21 May Apel described to Schultz (and through hidden microphones to the British listening post) how Tippelskirch erred by placing a man on lookout duty who had no previous experience of watchkeeping in that boat; and how the I.W.O. Falow erred by taking more interest in events occurring in the port quarter than in the seascape on the starboard sector which was his responsibility—though Falow did take the ultimate responsibility for the dereliction, as Apel explained:

APEL: Do you know what our First Officer of the Watch did? Anyone else would have fetched it [a lifebelt] for him, and someone else did fetch it, and brought it to him. He said: “I won’t take anything.” Well, of course, we were absolutely staggered that he wouldn’t take the lifebelt. Then he went and stood forward on the bridge. He gripped the bridge with both hands and went down with the boat like that. At the time of the mishap he was on the bridge. The boat which we had rammed appeared in his sector. Of course, he would have been definitely held responsible in Germany. To be quite honest, it was our fault—or rather it was the fault [of those] on the bridge. We had a new Bootsmaat [Petty Officer Third Class (USN)] on the patrol. He’d never been on watch at all. At six o’clock in the evening, the Commander sent for him and said: “You’ve been on watch on the bridge in the other boat, haven’t you?”—“Yes.”—“Can you see well at night, too? Have you sighted anything yet? You’re sure you can do it?”—“Yes.”—“Good, you can do watch on the bridge tonight.” He [the Bootsmaat] stood forward…. And suddenly on the port side of the boat, aft, tracers were seen, so there must have been some firing— so [the port quarter lookout] naturally thought that must be the convoy, and reported it at once. The Officer of the Watch was interested, turned round and had a look. The Commander was on the bridge and looked, too. The [new Bootsmaat] forward, who should really have continued to look straight ahead, looked round too, and the Commander said to the two look-outs [forward]: “Pay attention, don’t look over there, that doesn’t concern you. Something may come from any side.” Until now that [policy] had always been so, and had always been successful, and this time apparently he didn’t say that to the new [Bootsmaat]. He should have known it himself. There was more firing. The others kept their eyes glued to their sector, when suddenly the Officer of the Watch turned round and yelled: ”Verdammte Scheisse—A.K. zurück!” ['Hell and damnation!—full speed astern!"] But it was already too late.

SCHULTZ: Perhaps the boat didn’t sink at all. You can’t possibly tell.

APEL: She definitely went down. She heeled over almost vertically and went down like that. The diving tanks were still full of air. She probably stopped sinking at two hundred meters, three hundred meters, or even three hundred fifty meters for about half an hour, and then, in time, she would get heavier and heavier as more water came in.

SCHULTZ: Yes, but they can still blow the tanks or—

APEL: No, no. Our whole bow compartment was under water. Forward in the bow compartment the bulkhead was closed. It was a watertight bulkhead but will not stand up to heavy pressure. The lower bulkhead will certainly have caved in. Even before, it was never quite watertight, water already came.…

SCHULTZ: There’s no proof at all that the men are dead.

APEL: Oh yes. Just think, where could they blow the tanks? First, the diving tanks were still full of air, but there was water in the boat…. We were unlucky. We started up both pumps immediately and we were unable to get rid of a single drop of water that had broken in.

Another closemouthed survivor, but from the other boat involved in the collision, was Bruno Arendt, a twenty-three-year-old Bootsmann (the U.S. Navy equivalent: Petty Officer, First Class; Royal Navy: Chief Petty Officer). Quartered with Helmut Klotzsch, the Obersteuermann (Navigator) of U-175, sunk on 17 April 1943, Arendt was heard to say (and recorded) on 13 May:

ARENDT: The Interrogation Officer wanted to know the number of the boat, but I won’t tell him

KLOTZSCH: What number did you have?

ARENDT: Six-fifty-nine.

KLOTZSCH: Some two hundred boats have been sunk already.

ARENDT: They will make a fine mess of things this summer. There is no question of there being more boats operating now. As soon as they come out they’re sunk…. By the time you’ve sailed for three years you’re just about finished.

KLOTZSCH: Yes, I know an Obersteuermann who is now on his sixteenth patrol.

ARENDT: Well, let him get that over safely, and then he’ll go on his seventeenth and that will be the end of him! Twelve men [from our two boats] were saved altogether.

KLOTZSCH: Twelve men from two boats?

ARENDT: Yes. There were forty-eight in our boat. That’s ninety-six in the two boats.

KLOTZSCH: It’s a tragedy. The whole business of U-boat sailing has simply become a job for convicts.

Two sets of omens. Which would prevail? The triumphant auguries of Henke (U-515) ? Or the woeful auguries of Stock (U-659) and von Tippelskirch (U-439)? But pantomancers were probably few on either side. More dully, the slogging procession of May would tell.



Detection and Attack

In all the long history of sea warfare there has been no parallel to this battle, whose field was thousands of square miles of ocean, and to which no limits of time or space could be set. CAPTAIN STEPHEN W. ROSKILL, D.S.C., R.N.

On certain naval histories’.They are primarily accounts of what happened, and do not, in my view, adequately explain why it happened. SIR STUART MITCHELL

The months of July and August [1941] saw the North Atlantic U-boat operations sink to their lowest level of effectiveness, and it looked almost as though the defense had won the race against the attack. DR. JURGEN ROHWER

BY THE DATE OF THE EVENTS described in this narrative the major forces, directions, and trends in the Atlantic campaign had long been established. There is no need to review all the operational details of the war at sea from the outbreak of hostilities on 3 September 1939 to the beginning of May 1943, since these have already been essentially addressed in the historical literature. But before considering developments in Allied armed countermeasures to the U-boats, which is the intent of this chapter, it might be helpful to tease out of the previous forty-four months of data several findings that are surprising and provocative.

The first of these relates to numbers. At the outset of war, Dönitz had only thirty-nine operational U-boats, including twenty-two Type VIIs and Type IXs—instead of the 300 he had stated was the minimum number he would require to conduct a successful war against Great Britain’s Atlantic trade, and instead of the 162 oceangoing boats he had been promised by Hitler in the naval construction program scheduled for completion in 1948(!). Of these twenty-two, only six to eight could be deployed on operational stations at any one time, the remainder being in transit or in repair yards. Through February 1941 his available force declined in number rather than grew, despite the successes of the first year and five months, which included the sinking of the battleship Royal Oak by U-47 (Korvettenkapitän [hereafter Korv. Kapt.] Günther Prien) on 14 October 1939 and a five-months-long U-boat spree in waters adjacent to the United Kingdom and Ireland from June to October 1940 that added 1,395,298 enemy GRT to Dönitz’s bar graphs and became known among U-boat crews as glückliche Zeit—the “Happy Time.”

Those successes, gained mainly against nonconvoyed, independently routed ships, unquestionably impressed Hitler, but the Führers favor was not reflected in his allocations of steel and workers for U-boat construction, with the result that, owing to combat losses, in February 1941 Dönitz commanded fewer operational boats (22) than he had on the first day of war. In that month, however, the delivery rate improved, and by the end of July 1941 the number of operational boats surpassed Dönitz’s original number. The increase would be sustained thereafter with occasional slight diminutions (May-June 1942, October 1942-January 1943, and March-April 1943) until May 1943, when Dönitz would have no fewer than 433 boats in commission (207 operational in the North Atlantic theater).

One might have expected that after mid-1941 the U-boats’ success rate would increase at the same rate as that of new commissionings. But such was not the case. From July 1941 forward, sinkings decreased markedly. From 305,734 GRT of Allied shipping sunk in June 1941 the totals fell to 61,471 in July and 67,638 in August. Whereas in September 1940, when an average of thirteen operational U-boats were at sea, Dönitz’s commanders had sunk 265, 737 GRT, for an average of 753 GRT per boat per day at sea, one year later, in September 1941, when an average of 36.5 boats were at sea, his commanders sank only 208,822 GRT for an average of 186 GRT per boat per day. The tonnage sunk in October 1941 dropped to 182,412 GRT, that in November to 91,628 GRT, and the total in December was 101,687 GRT, with correspondingly low GRT averages per boat per day. In other words, during 1941 the more operational boats there were, the fewer their successes.

And 1941 is not the only period in which we notice that discrepancy. As indicated in the prologue, the greatest monthly toll of Allied shipping lost to U-boats in the war (743,321 GRT) was taken in November 1942, a month in which the U-Bootwaffe had 95 operational boats at sea. Their average sinkings per boat per day were 220 GRT. Two years earlier, in November 1940, when there were only 11 operational boats at sea, the average sinkings per boat per day were 430 GRT. With nearly nine times the number of boats, the U-Bootwaffe in its best month of the war scored slightly more than half the successes per boat of those achieved by their forerunners.

In January, February, and March 1943, which are closer to the special focus of this narrative, there were 92, 116, and 116 U-boats, respectively, operating in the Atlantic, where sinkings were, again respectively, 218,449, 380,835, and 590,234 GRT. Taken alone, these were impressive figures, augmented in no small part by the mauling of SC.122/HX.229 in March; but considered in terms of the large operating force at sea in those months we find that the tonnage numbers credited to each boat per day at sea were 65, 99, and 147 GRT, which, taken together, represented no improvement over the figures posted during the second half of 1941.1 Dönitz was still sinking fewer merchant ships per investment of U-boat days.

Returning to 1941, where we first notice a sharp falloff in U-boat productivity, we can ask, how may it be explained? One reason that has been offered is the sudden loss of three individual U-boat “aces” in March: Prien (U-47) and Kptlt. Joachim Schepke (U-100), both of whom were killed, and Korv. Kapt. Otto Kretschmer (U-99), who was captured. These commanders, who had first made their reputations in the “Happy Time,” had achieved tonnage totals ranging from Schepke’s 156,941 GRT to Kretschmer’s 257,451. All were Ritterkreuzträger, winners of the Knights Cross of the Iron Cross, with Oak Leaves, and, as such, were inspirational role models for the rest of the officer corps.

Fregattenkapitän (hereafter Freg. Kapt.) Günter Hessler, Dönitz’s son-in-law and a member of his operations staff, stated after the war that the U-boat successes prior to July 1941 were not “due only to the skill of such men as Prien, Kretschmer and Schepke, for there were equally competent commanders in 1941, who however had to contend with much greater difficulties.” He may have had in mind such men as Kptlt. Engelbert Endrass (U-45, U-567), Korv. Kapt. Reinhard Suhren (U-564), and Kptlt. Adalbert Schnee (U-201). Endrass would be lost in December 1941 (in a convoy battle I personally made an long entry in this forum a yerar ago). Postwar analysis, however, would place an emphasis on how important for the U-Bootwaffe’s overall success was the performance of certain individual commanders, whose loss would be a pronounced negative. No more than thirty-commanders (2 percent of the whole), it was found, accounted for some 30 percent of Allied shipping sunk by U-boats during the war; and, significantly, for what it said later about replacement commanders, all had entered the Kriegsmarine before 1935. Only fourteen commanders accounted for nearly 20 percent of all sinkings. Only 131 boats sank or damaged six or more ships. Meanwhile, 850 boats, which represented three-quarters of all boats commissioned during the war, failed so much as to damage a single merchant vessel.

With these figures in hand, Günter Hessler notwithstanding, the argument that the loss of three proven performers in Prien, Schepke, and Kretschmer had an adverse effect on U-boat fortunes in July-December 1941 is, though not decisive, persuasive. As has been written, “One cannot leave the subject of human factors without re-emphasizing the importance of the aces on both sides…. Kretschmer, Prien et alia were good enough to distort all statistics. The difference was that [Allied] escort commanders lived to improve their skill and to pass it on, whilst U-boat aces had a short life.”

Another reason more frequently, and convincingly, offered is the acquisition by the British, in February-June 1941, of access to secretly encrypted radio traffic between Donitz and his boats. The story is now a familiar one. For secret radio communications the three German armed forces, land, sea, and air, employed a once commercially available electrical-mechanical encryption machine. Called Enigma, it resembled a typewriter with a standard keyboard, which was used for punching in the message to be encrypted. Above the keyboard were three (later four) rotors, and below the keyboard facing the operator was a plug board. By altering the rotor settings and plug pairings each day, it was estimated that the possible permutations created by the machine approached one hundred and fifty million million million, a number maintained by German cipher experts to be beyond solution. But in 1934 Polish Intelligence Service mathematicians, by yoking six Enigma machines together, did find a partial solution. They managed to pass on their findings to French cryptanalysts, thence, after France, too, fell, to the cryptanalysis establishment at the (mostly) fictitious Government Code and Cipher School (GC&CS) in England.

Housed in a red-brick mansion in pseudo-Tudor-Gothic style at Bletchley, halfway between Oxford and Cambridge, GC&CS had already made substantial progress against Enigma on its own. Under the direction of academics, notably the Cambridge mathematician Alan Turing, GC&CS constructed an electromagnetic scanning machine called the Bombe. Fed to the Bombe’s innards, intercepted German signals traffic began to shed its veils. First to be read was Luftwaffe (Air Force) Enigma, on 22 May 1940. Shortly afterward, the machine decrypted Wehrmacht (Army) traffic. Single-story white-frame Nissen huts sprang up behind the mansion to house academics who translated and interpreted the incoming German messages. Hut 8, however, which was assigned to naval traffic, was frustrated by the Bombe’s inability to penetrate the Kriegsmarine’s more complex U-boat cipher, generated by the marine version of the Enigma machine, Schülssel M (Marine-Funkschlüssel-Maschine M). Naval Enigma, in fact, would resist for a full year until finally forced to submit in winter-spring 1941.

What Hut 8 had needed to resolve the impasse were operational wired rotors and operators’ handbooks that gave daily Schlüssel-M settings and pairings. In a series of “pinches” conducted from February through June 1941, the Royal Navy obliged. On 12 January 1940, off a captured crewman of the sunken U-33 in the North Channel between northern Ireland and Scotland came rotors. On 4 March 1941, from the wrecked German whaling trawler Krebs off the coast of Norway during Operation Claymore , the large scale British commando raid on Loforten islands , came key tables and settings. Armed with these materials, Hut 8 could then read U-boat traffic in the Heimische Gewässer (Home Waters) key for the entire month of April. More pinches were to follow. From the captured German weather ship München east of Iceland on 7 May 1941 came settings and keys for June. And, the pièce de resistance, two days later, Royal Navy destroyer HMS Bulldog boarded U-110 (Kptlt. Fritz-Julius Lemp) in mid-Atlantic and came away with a Schlüssel-M including spare rotors, a Home Waters handbook with daily settings and pairings, special settings for Offizier, officer-only, signals, and short-signals (Kurzsignale) code books, all valid to the end of June.

Included also was the first captured naval grid chart of the North Atlantic and most of the Mediterranean. This chart, Nr. 1870G Nordatlantischer Ozean, with land surfaces in green and water surfaces in white, was divided into blue-lined squares, each identified by a digraph; for example, going west to Newfoundland a U-boat would pass through naval squares BF, BE, BD, BC, and BB. Each artificial square, about 486 nautical miles per side (along 50° latitude) was subdivided into nine smaller squares identified by double-digit numerals, from 11 to 99. Each smaller square was then subdivided nine times, then nine times again to form a fine screen that could take positions at sea down to a Marinequadrat (naval square) no larger than six nautical miles to a side. Typically, a U-boat’s position in radio messages and war diaries would read as follows: ET 6278, which was Werner Henke’s position in U-515 when he sank his first four ships southwest of Freetown on the night of 30 April/1 May. The naval square coordinates would be used by the U-Bootwaffe throughout the war in the place of latitude and longitude. A square was usually cited as quadrat, or qu.

When this godsend was received at GC&CS, Hut 8 began reading the other side’s mail much closer to the grain. More help was to come. In a tightly planned operation on 28 June 1941, Royal Navy cruisers and destroyers boarded a second German weather ship, Lauenburg, in the Norwegian Sea and captured the Home Waters key for July, allowing for continued Hut 8 penetration during that month. By mid-August 1941 Hut 8 had no further need of pinches and was able on its own to decrypt the key within fifty hours of transmission (41 hours in September, 26 in October). There had been brief blind spots on 1–4 August and 18–19 September, but from November forward the key would be read daily with virtual currency until war’s end. The only downside to that success was that beginning in February 1942, Home Waters’ use for U-boat operations would cease, to be replaced by a new, more intricate cipher key named Triton. Employing a fourth rotor in the Enigma machine, Triton would remain impenetrable for nearly eleven months.

In the meantime, from July forward, GC&CS was able to send U-boat decrypts by secure circuit to Commander Winn and Lieutenant Beesly in the Submarine Tracking Room of the Operational Intelligence Centre of the Admiralty, where U-boat positions for the first time could be established confidently on the Main North Atlantic Plotting Table that depicted latitudes and longitudes 73°N to 5°S and 100°W to 60°E. When received there, the decrypts were given the designation “Special Intelligence,” or “Z.” When the essential information contained in the decrypts, though never the raw decrypts themselves, was signaled by OIC to headquarters, base, and fleet commanders, it became known as “Ultra.”

The confidence and authority of the Tracking Room advanced dramatically. By Winn’s order, a large photograph of Admiral Dönitz looked down upon what Winn fancied was a shadow BdU.5 Now, as he and Beesly observed the proceedings of individual U-boats, as revealed in their daily position reports back to BdU, and followed the organization of anti-convoy patrol line groups, as ordered by the BdU Operations transmitter, the two RN Reservists could do for British trade convoys what had not been possible in any reliable way before: provide evasive routing around known U-boat concentrations. Noting this watershed in anti-U-boat warfare, numerous historians have credited the newly acquired signals intelligence with causing the precipitous decline in merchant ship sinkings that occurred in July and the remainder of 1941.


Before considering a third possible reason for the U-boat failures of July-December 1941, it would be well to remark that Germany’s own radio monitoring and cryptanalysis service, B-Dienst (.Funkbeobach tungsdienst), was not itself idle during this same period. Since before the war, in fact, its staff—500 in 1939,5,000 in 1942—at Tirpitzufer 72–76 in Berlin had been busily attacking various of the British codes and ciphers, gaining entry early on to the Royal Navy Administrative Code, Auxiliary Code, Merchant Navy Code, and Naval Code No. 1. It also had modest success against Naval Cipher No. 2, adopted on 20 August 1940. But it was Naval Cipher No. 3, introduced at the start of October 1941, that most engaged the energies of the B-Dienst cryptanalysts, since its content dealt specifically with Allied convoys. Originated in June 1941 for use by the British, United States, and Canadian navies in the Atlantic, and popularly called the Anglo-American Convoy Cipher, it quickly became the conduit for information about convoy departures, routes, diversions, and arrivals, as well as about stragglers.

By December 1941 B-Dienst was making its first breaks into the cipher, and two months later it was reading as much as 80 percent of the transmitted signals. This was a perilous development for the convoy system, since Admiral Dönitz, often with movement and diversion information ten to twenty hours in advance, could place his U-boat patrol lines directly athwart convoy courses. Since the same intelligence source conveyed to him the Admiralty’s daily U-boat dispositions signal, Dönitz also knew what (in general) Winn’s Tracking Room knew about his U-boat positions, though he never tumbled to the conclusion that the accurate Admiralty signals on the point were based on cracked Enigma.

There were occasions when U-boats were lost under suspicious circumstances, or when German surface refueling tankers were swept from the sea in a flash (as five German supply tankers were intercepted and sunk by Royal Navy cruisers in 3–15 June 1941), or when a convoy suddenly altered course around a patrol line, or when an ocean-full of U-boats failed to sight targets and Dönitz became sufficiently troubled about cryptographic security that he consulted Konteradmiral Ludwig Stummel, whose Second Department (Operations) of the Naval Staff in Berlin superintended naval ciphers. Stummel always assured Dönitz that Admiralty information had to have come from shore-based radio direction finding, from air reconnaissance, or from surface ship sightings. The Enigma cipher, with its variable range and changes of settings, was invulnerable to enemy penetration by all known methods of mathematical analysis, Stummel insisted, and even if an entry should be made by accident, the information developed would be long out of date and operationally useless.

Dönitz’s own staff analyzed the suspicious cases and came to the same conclusion that ordinary noncryptographic means could account for them. Nonetheless, Dönitz took the precaution of introducing a series of complex position-disguising devices into the cipher transmissions, all of which were eventually solved by GC&CS. He also restricted the number of staff who had authorized access to U-boat positions information as well as the number who were permitted to tune in the U-boat wavelength.

As a result of each belligerent having the other side’s key, sea warfare in the Atlantic during the winter and spring of 1943 became in part a backroom chess game as the Tracking Room, playing Ultra, sought to outwit BdU, playing B-Dienst, and no doubt on numerous occasions one side was able to neutralize the other’s advantage. After the war, in a secret report (“three copies only”) dated 10 November 1945, Paymaster Commander WGS Tighe, R.N., of the Signals Division, Admiralty, presented a report titled “German Success Against British Codes and Ciphers.” It exists today in nineteen-page summary form. In it Tighe described the Signals Division as “shocked” to have learned after the war from captured documents and interrogations of German cryptanalysts that Naval Cipher No. 3 had been thoroughly compromised, and that this security failure “not only cost us dearly in men and ships, but very nearly lost us the war.” That extravagance was matched by Tighe’s subsequent claim that “all successes obtained by U-boats against convoys HX229 and SC122 in March 1943, when 22 ships were sunk, can be directly traced to the information obtained by reading our signals.”

Certainly B-Dienst was at concert pitch prior to that battle of 16–20 March—called by the RN official history the “biggest convoy disaster of the war”—and Tracking Room records show that B-Dienst, hence Dönitz, had prior information about the ocean course of SC.122 and about both the original route and a diversion of HX.229. What the Germans did not know was how far along their courses the two convoys had proceeded by 15 March. That was the date, at 1918 GMT, when U-91 (Kptlt. Heinz Walkerling), en route to a refueling rendezvous, sighted and followed a destroyer that was proceeding on a northeast course in qu BC 3486 (49°33’N, 40°35W). Thinking that it might be overhauling a convoy, Walkerling trailed it and was rewarded with the chance sighting of HX.229.

Various sources state that knowledge of the German reconstruction of Naval Cipher No. 3 was smelled out by American Naval Intelligence in March and May 1943.12 But GC&CS had learned from Enigma solutions as early as December 1942 that B-Dienst was reading the cipher.13 This is confirmed by Francis Harry (now Sir Harry) Hinsley, O.B.E., M.A., F.B.A., who was a team member of Hut 8 from its beginning, where his long tousled hair and worn corduroy trousers caused him to become known to Commander Winn, a frequent contact, as “Professor Corduroy.” Four decades later, in 1981–1984, Hinsley published the official history of British Intelligence in World War II. In June 1996, when the writer brought the Tighe Report to Hinsley’s attention, the quondam cryptanalyst, later President of St. John’s College and Professor of the History of International Relations at Cambridge University, recalled how dismayed Hut 8 was to learn that B-Dienst was looking over the Admiralty’s shoulder and that no one there was doing anything about it!“

We had a watch on to see if the Germans were reading Allied ciphers,” he told the writer. “It was awkward for OIC and Bletchley Park to know the Germans were reading the Anglo-American Convoy Cipher from December to August.” The responsible person for doing something about it was Paymaster Captain D. A. “Willie” Wilson, R.N., in charge of naval cipher security under the Director of the Signals Division, Admiralty. “Wilson was slow to conclude that the Germans were reading the cipher, for which he was criticized at the time and after the war.” When he finally acknowledged the security breach, Wilson dawdled in replacing the compromised cipher. “His argument was that there was a large number of holders of the cipher spread all over the yard, that it couldn’t be replaced partially, and that he couldn’t replace it any faster than he was doing. Well, there was a certain amount of muttered criticism about the delay at Bletchley Park and at the OIC. The delay is an extraordinary story.”

As for Tighe, unlike Wilson he probably was not “indoctrinated,” that is, “in the know” about Ultra, “thus accounting for his naivete.” His report “was probably an attempt [by the Signals Division, Admiralty] to defend themselves, to cover-up and justify themselves.” A temporary modification of the cipher was introduced, finally, in June, and the cipher was completely changed to a secure key in August 1943, after which there were no further German entries. With that closure the Allies won the cryptographic war.

The paper victory did not mean, however, that Ultra was the one decisive factor either in the improvement of Allied fortunes at sea after June 1941 or in the pivotal defeat of the U-boats to come in spring 1943, despite the “Ultra Myth’s” persistence in claiming so.15 Several features of Sigint (signals intelligence) work against that judgment. For one thing, there were frequent time delays between the interception of an Enigma transmission and its decryption. As we have seen, the average intervals in August, September, and October 1941 were fifty, forty-one, and twenty-six hours, respectively. Following the decryption of the Triton key in December 1942, the delays in decryption were frequently longer than those. When one reflects that a fast convoy might cover 240 nautical miles in a twenty-four-hour period and that U-boats might proceed between 320 and 370 nautical miles in the same period, it becomes evident that a much-delayed Ultra message might have little or no operational value.

Too, at some critical times when the Germans changed Enigma settings, GC&CS went completely blind so far as decryption was concerned (though it and the Tracking Room had other, less accurate resources to fall back on, as discussed below). Such was the case during the eleven-month drought following introduction of the fourth rotor. During the critical months January through May 1943 there were numerous failures of shorter duration, including ten days in January, seven days in February, the periods of 10–19 March, when the battle of SC.122/HX.229 was fought, and 26 April-5 May, when the protracted and definitive battle for Convoy ONS.5 was waged across 720 miles at sea (see chapters 4 through 7). And even when Triton decrypts were in hand, they were “not uncommonly” seventy-two hours old, making their operational value marginal. For all the above reasons, one has to look for another component reason for the Allies’ post-June 1941 success in protecting merchant shipping.

Here Sir Harry Hinsley helps us and in so doing sets aside any pro-Sigint bias he might be expected to have. Though he does say that “The difference between what the U-boats now [post-June 1941] achieved over-all and what they might have achieved—and, indeed, expected to achieve—was due to the great improvement in the evasive routing of the convoys that took place when GC and CS began to read the naval Enigma,” he stresses the fact that:

“For the reduction in actual shipping losses the main cause was a change in the Admiralty’s policy. From 18 June it raised the minimum speed limit for independently routed ships from 13 to 15 knots, and there followed a dramatic decline in losses of “independents,” from 120 ships in the three months April to June to 25 ships between the beginning of July and the end of September.”

Cryptanalyst and historian David Kahn agrees that Sigint was not the main cause for the reduction in shipping losses:

“… Intelligence did not always rule in the war against the U-boats. Other factors outweighed it. The July-August loss of tonnage fell to under a third of the May-June figure for reasons unrelated to B[letchley] P[ark]. More escorts were available and were accompanying convoys uninterruptedly across the Atlantic. The escorts’ experience made them more efficient. The minimum speed of ships sailing independently was raised from 13 to 15 knots. Air cover was increased.”

It appears that all three factors examined above—loss of the U-boat aces, Allied signals intelligence, and improvements in the convoy system, especially the inclusion of 13-to-15-knot ships—had a cumulative effect in producing the turnaround of 1941; but that the last-named factor had the single most pronounced effect, as discussed below.

Whereas in World War I it took Great Britain nearly three years to institute a convoy system, thus finally stanching a trade hemorrhage that sorely threatened the island nation, in September 1939 she had in place detailed plans in the event of war for the immediate deployment of RN vessels to escort merchant ships in convoy. The first formation of ships in column sailed on 6 September. By the end of the first month of war, 900 ships had sailed in convoy without a loss, while thirty-nine Merchant Navy vessels that had been independently routed were sunk by U-boats. In the beginning there were few available escort ships—destroyers, frigates, sloops, and corvettes—that were equipped for antisubmarine warfare. The majority of destroyers were assigned to the Home Fleet for use against the Kriegsmarine’s high seas fleet. Still, the Trade Division of the Admiralty was able in September 1939 to develop three major convoy routes that could be protected with the naval assets at hand:

  1. OA and OB: Outward bound from Britain to North America and Africa

  2. HX: Homeward bound to Britain from Halifax, Nova Scotia

  3. SL: Homeward bound from Sierra Leone


During the first four months of the war, 5,756 individual ship sailings were made in convoy, suffering only four sinkings by U-boats. The German opportunities to attack the convoys were greatly improved in the following summer, however, by their not having to sortie any longer from Baltic and North Sea bases, which required a lengthy roundabout the north of Scotland before reaching the North Atlantic sea lanes. With the surrender of France to German ground forces in June 1940, Admiral Donitz was able to base his boats on the Brittany peninsula and Western French coast directly abutting the Bay of Biscay and the Atlantic. There, at Brest, Lorient, St.-Nazaire, La Pallice, La Rochelle, and Bordeaux, the Organisation Todt erected bombproof U-boat shelters, some of them with steel-reinforced walls three meters thick and even stouter carapaces seven meters in depth.

Outside Lorient harbor, at Kernevel, Dönitz established his headquarters, BdU, in a requisitioned chateau. Kptlt. Fritz-Julius Lemp, later of the ill-fated U-110, was the first commander to put in at Lorient, in U—30, on 7 July 1940. With establishment of the Biscay bases in close proximity to Allied shipping, not only that which moved eastwest but also north-south convoys and independent shipping to and from Gibraltar and Freetown, and with replenishment and repair facilities readily available to the operational fleet, Dönitz effectively multiplied both his force and their time at sea by a factor of three.

In these circumstances, a year later Dönitz was able finally to institute full-scale a tactic that he had first conceived while commander of the submarine UB-68 in the Mediterranean in 1918. Instead of individual operations against convoys and independents, he envisioned group operations led by a flotilla commander employing the new technology of radio telegraphy. Twenty-one years later, in May 1939, when a Rear Admiral in Hitler’s Kriegsmarine and Führer der Uboote (FdU), Dönitz tested his concept in sea exercises, which proved the feasibility of radio-controlled mass attacks, what he called die Rudeltaktik (pack tactics, later known to the British as wolfpack operations).’

In the original theory, pack attacks would be directed by a Type IXB command boat at sea, but soon after war operations began, Dönitz abandoned that plan and established the principle of shore direction in its stead: At headquarters, it was thought, where contact could be maintained with every boat, and where intelligence was readily available, Dönitz and his operations staff could best command the formation of U-boat patrol lines (or “rakes”) that would stand at right angles to convoy courses, with average spacings of 8 to 15 miles between boats, and vector them toward known or suspected targets.

First attempts at this battle management system in October and November 1939 were unsuccessful, in part because the U-boats were too few in number to form effective packs. Subsequent efforts in 1940 were little better in practice and result. By spring 1941, however, when the number of boats had increased and the high degree of coordination required by the management plan was more precisely fixed in the minds of U-boat Commanders, Donitz launched the Rudeltaktik in earnest. The plan called for the first boat on a line that sighted a convoy to report its position, course, and speed to BdU by radio. That boat thereafter would not normally attack the convoy but rather shadow it, constantly updating its position and course as the contact-keeper.

From BdU, radio orders would direct the other boats in line to converge on the convoy and attack it in concentration at night on the surface, when the U-boats could take advantage of the darkness, of their low nap-of-the-water silhouettes, and of their high speed under diesel engine power. The strength of the Rudeltaktik was that it enabled U-boats to fall upon a convoy all together like a pack of wolves on a flock of sheep. Its weakness was that the high-frequency radio signals of both the shadowing boat and of BdU were vulnerable to interception, to radio direction-fixing, and, after May—June 1941, to decryption. But it was the system that Donitz would stick to like paste up to and through the climactic events of May 1943.

Typically, a transatlantic convoy crossed 3,000 miles at sea in nineteen to twenty days westward, fifteen to eighteen eastward. The average number of ships sailing in each convoy by May 1940 was forty-six, and the forties range remained the rule until 1943, when the optimum convoy size was raised in number. Until May 1941, the U-boats operated east of 40° W longitude in the Western Approaches north and south of Ireland. It was possible for the RN to give adequate surface escort to that distance from bases in Britain, Northern Ireland, and Iceland.

When in May 1941, however, the U-boats moved farther to the west outside the escorts’ radius of action and sank nine ships for 54,451 GRT from Convoy HX.126 in qu AJ (40"52’ to 4i°36’W longitude), on the 20th/21st, the Admiralty decided that the time had come to provide complete transatlantic—what came to be called “end-to-end”—escort. Here the Royal Canadian Navy (RCN), then in the middle of a huge expansion, played a central role. An RCN escort group out of St. John’s, Newfoundland, covered HX convoys as far as 35°W, where they were relieved by a British group from Iceland, which in turn was relieved by a U.K.-based group for the final leg from 20°W to the North Channel. The number of RN escorts rose from 108 in June 1941 to 134 in November. The number of RCN escorts in the western Atlantic similarly increased.19 Also, beginning in September, U.S. Navy (hereafter USN) destroyers escorted Britain-bound convoys as far as a midocean meeting point (MOMP), or “chop” (Change of Operational Control) line, south of Iceland, where RN escorts took the guard. And by August the Germans were remarking on a higher efficiency of escorts on both the transatlantic and Gibraltar runs: “Not only had the numbers of escort vessels and aircraft risen, but their methods of keeping the U-boats at a distance had improved. Where a few months ago one U-boat had been adequate for shadowing, a whole group was now required.”

The Admiralty introduced oilers to enable the escorts, particularly short-legged destroyers whose fuel bunkers had been designed for close-in warfare in the North Sea and English Channel, to extend their range and stay with their convoys. Also, as earlier noted, in what historian J. David Brown has called one of the most important decisions taken by the Admiralty at this time, on 18 June 1941 the Trade Division required all ships with speeds of 13–15 knots, which previously had sailed independently, to form up with slower-moving convoys; only those ships whose speed exceeded 15 knots would be routed independently thereafter on the expectation that at that and higher speeds, those ships could evade U-boats, whose maximum sustained speeds were in the range of 17–18 knots. Whereas in the second quarter of the year 120 ships proceeding independently were lost to U-boats, during the second half of 1941 only 49 independents went down, because fewer independents were being sailed.

All the while, the U-boats were not going unscathed. By 31 December 1941 sixty-seven boats had been sunk in the year, forty-five by RN ships, one by an RCN vessel, three by Allied submarines, five by mines, four (and another shared) by RAF aircraft, and the remainder by miscellaneous causes. Where in 1940, when there was a monthly average of 13.5 U-boats at sea, there was a yearly total of 22 U-boat casualties, for a monthly average loss of 1.8 percent, in 1941, when there was a monthly average of 25.5 boats at sea, there was a total of 67 casualties, for a monthly average loss of 5.5 percent. During the last quarter of 1941, one Atlantic boat was lost for every three ships in convoy sunk—an insupportably poor exchange rate. By any measure, at year’s end the Allies were ruling the convoy lanes. The improvement in the performance of surface escorts was due to higher experience levels, better skill in the use of detection gear and weapons, tighter training programs, and closer coordination by voice radio with RAF Coastal Command aircraft—though it must be said that that Command had not yet come into its own as an anti-submarine force.

The principal weapon of the surface escort against a submerged U-boat was the depth charge (D/C in short term) , a canister of high explosive, first Amatol, then Minol, and finally, in the summer of 1942, Torpex—though Minol fillings continued in use through 1943. Torpex was a high-explosive mix of Cyclonite, TNT, and aluminum flakes. The standard Mark VII “heavy” D/C weighed 250 pounds, sank at 16 feet per second, and, when detonated by a preset-to-depth hydrostatic fuse, caused the formation of a spherically shaped gas bubble with an initial temperature of about 3,000° Centigrade and, on the periphery of the bubble, a pressure pulse, or shock wave, equivalent to 50,000 atmospheres. The pressure pulse rose to peak level within a few milliseconds and moved through the water at the velocity of sound, its energy dissipating directly with the square of the distance traveled. Because of the greater density and incompressibility of water, the shock wave traveled farther and faster underwater than it did in an above-water explosion. Such a wave was considered able to fracture a U-boat’s hull if initiated within 20–26 feet of it and to cause damage within 50 feet.

Surface evidence of the shock wave was given by a breaking of the water’s top layer and a “dome” of spray. Evidence of the expanding gas bubble was provided by the familiar towering “plume” that broke through later.22 An escort vessel both “fired” and “dropped” D/Cs, though the verb fired was normally used for both. Firing was done laterally by mortar “throwers,” two to each side, port and starboard. The drops came by gravity off racks, or rails, at the stern. In 1941 and 1942 escort Captains used the throwers and rails in various combinations, usually in salvos of five, but by 1943 experience had shown that the most effective D/C attack was made in a “10 Pattern,” with four fired and six dropped, five set to explode above the target and five below. In order, the forward throwers fired first, then the aft throwers, after which six D/Cs were rolled off the stern. The resulting pattern formed a fore-to-aft oval.

In December 1942 a Mark X “One Ton” D/C was distributed, usually one to a ship. Filled with a 2,000-pound charge, and theoretically the equivalent of a 10 Pattern, the Mark X was designed to reach deepdiving boats. It was housed in a ten-foot-long cylinder and fired by cordite charge from a torpedo tube. Escorts had still other weapons available to them, including 4-inch deck guns and Oerlikon anti-aircraft guns that, on several occasions, at maximum depression, were used with effect against surfaced boats. A weapon of last resort was ramming and, though this action usually brought damage to the escort’s bows, requiring seven to eight weeks to repair, by May 1943 about twenty-four boats had been dispatched by this means.

Detection of a submerged U-boat, whose principal advantage was underwater stealth, was made possible by the development between the wars of a sound-ranging device called asdic (an acronym that grew out of Anti-Submarine Division, the Admiralty department that initiated the system). An asdic apparatus, housed in a dome on the underside of a vessel’s hull, sent out sound waves in pulses that, when they struck an undersea object such as a U-boat, returned a pulse echo that gave the object’s bearing and range, though not (before 1943) its depth. When the pulses bounced off a U-boat’s hull they emitted within the boat a loud, piercing PING-ping! A similar system in the U.S. Navy was called Sonar (Sound Navigation and Ranging), a name later adopted by the RN.

Early wartime Types 123 through 129 had serious limitations, including short range of effectiveness, about 1,300 yards (1.2 kilometers) in good sea conditions, and inutility above vessel speed of around 15 knots. Range and accuracy improved in 1942 with the introduction of the Types 144/145 series, and depth determination became possible with the Type 147 in 1943, but upgrading in the fleet was slow and erratic: in 1944 58 percent of British corvettes still mounted old equipment. Another failing of early asdic was its inability to hold a target during the final 200 yards of an attack approach, when a U-boat could use the blind zone for evasive maneuvers. This problem would be met later by the development of thrown-ahead weapons such as the “Hedgehog,” a bank of twenty-four contact-fused projectiles with Torpex warheads equivalent to 50 pounds of TNT fired from mortar spigots to form ahead of the attacking ship a circle 120 feet across or an ellipse 120 feet by 140 feet. (called H.H. in short nickname) The Hedgehog had teething troubles well into the summer of 1943.


Hedgehog Anti Submarine mortar

Again, the early asdic series could not track very deep-diving boats. Diving beneath the D/C spread—a submerged boat could alter depth at the rate of one and a half feet per second—was, of course, another defense of boats that were being “pinged.” Numerous efforts were made by the British to determine the maximum diving depth of the VIIC, the most numerous U-boat type. In 1942 RN submariners tested the captured U-570 (renamed H.M.S. Graph) and found that her thick hull survived the atmospheres of pressure at 200 meters (656 feet). The deepest measurement taken by asdic during the war was 238 meters (780 feet). Günter Hessler, who commanded U—107 until November 1941, then served on Dönitz’s BdU staff, wrote after the war that by the summer of 1942 new Type VIICs had been strengthened to a standard of 200 meters, “which in practice meant that in an emergency they could go down to 300 metres without harm.”

From interrogations of U-boat prisoners the British learned that most Commanders considered 200 meters the deepest safe depth when under attack, but that “good evidence” indicated that in the summer of 1943 one boat involuntarily dived to 340 meters (1,115 feet) without breaking up.26 Interesting is the finding that as late as early 1943 the maximum depth setting for British D/Cs was 550 feet. In June of that year both the D/C and asdic recorder settings would be readjusted to 750 feet.

Another defense against asdic was discovered by U-boats that operated in warm waters, such as those around Freetown, where temperature gradients and heavy density layers refracted the asdic sound beam. Boats in those climes frequently carried Bathy thermographs and thermometers to measure density and temperature. Efforts were made for a time to cover U-boat hulls with sound-absorbing (anechoic) coatings, such as layers of synthetic rubber, but these tended to separate from the hulls underwater. After 1943, the Pillenwerfer decoy that mimicked a U-boat’s asdic signature came into use. Called by the British SBT, for “submarine bubble target,” the decoy consisted of a canister containing metallic calcium-zinc “pills” that on contact with sea water created hydrogen bubbles. These bubbles returned an echo to asdic pulses that represented the dimensions of a U-boat. The canister was ejected through a six-inch-diameter tube (”Rohr 6” in Type VIICs) that projected through the pressure hull in the maneuvering room. The device remained suspended at a depth of about 30 meters (98 feet), and its bubble screen lasted for 15–20 minutes. Because it did not move laterally, the asdic operator was usually not fooled by it. More sophisticated decoys that did move were introduced later in the war.


All the while, the best way to defeat asdic was to employ the night surface attack, whether delivered singly or in a pack, since asdic was effectively blind to surface targets. By this means Admiral Donitz neutralized the early advantage that asdic had given the British, and he might thereby have earned an advantage for himself had not the British and Americans presented him with two other shipborne electronic marvels: high-frequency (radio) direction-finding (HF/DF, or “Huff-Duff“) and, more widely fitted, radar.

By use of a transformer circuit called a radiogoniometer, HF/DF receivers could determine the direction from which a radio signal was transmitted. Both Britain and the United States had ground-based HF/DF stations in operation during the early years of the war, and these took bearings around the clock on U-boat radio transmissions. By 1942 British DF receivers and antennas covered the North Atlantic sea lanes at listening posts ranging from the Shetlands around to Land’s End; south to Gibraltar, Ascension, Freetown, and Cape Town; and west to Iceland, Newfoundland, and Bermuda.

All of the bearings taken by these stations were communicated to the main station at Scarborough, England, and thence to the OIC Tracking Room at the Admiralty, where retired Lt.-Cmdr. Peter Kemp, R.N., headed a plotting team of never more than seven men and women who graphically presented the bearings taken on a particular boat’s transmitter by black strings drawn across a chart of the North Atlantic. Where the strings from three or more stations converged, that, it was estimated, marked the position of the U-boat. With as many as six bearings establishing the intersection, or “cut,” it was thought that a boat could be “fixed” within 25 nautical miles. Until naval Enigma gave more precise data in June 1941, this was the most reliable information on U-boats at sea that the OIC possessed, and convoys were vectored around estimated U-boat positions on the strength of DF intelligence. The network would play a critical role again during the Triton blackout of February-December 1942.

In the United States the USN had two similar HF/DF networks at work in 1942, one on the Pacific coast to monitor Japanese traffic, and another of seven stations that dotted the eastern seaboard from Winter Harbor, Maine, to San Juan, Puerto Rico. Analysis of U-boat transmission bearings received by the eastern net was done in the Atlantic Section, Intelligence Center (Op-20-G, later F-21), a clone of the OIC Tracking Room in the Navy Department (Main Navy) at Washington, D.C. Exchanges of data took place freely between the two rooms, and they with a similar Canadian Navy room at Ottawa. Early USN DF technology lagged behind that of the British, and the bearing computation experience of operators was so small that USN fixes were often qualified as being within 200 miles of the U-boat targeted. An intense training program improved the performance of the operators. And the equipment deficit was corrected by the gift of two superior systems, one British and one French. In the spring of 1941, an US Army Navy technical mission to England returned with a complete Marconi Adcock HF/DF installation, which the naval members of the mission judged to be “far ahead of us in these developments.” And an even more advanced system, antedating that of the British, instantaneous, automatic-indicating HF/DF, invented by French engineer Henri Busignies and smuggled out of German-occupied France, made its way, along with the inventor, to the United States in December 1940, where it was reconstructed by the International Telephone and Telegraph Corporation (ITT) and first supplied in prototype models to the USN net in the fall of 1941. Busignies’s system became the basis for future U.S. development in the field.

There were problems with the usefulness of shore-based HF/DF that were shared with Ultra, namely, that (a) they gave the Allies information at too great a distance for tactical attack purposes, and with a wide margin for inaccuracy since, many more times than not, they gave no indication of the direction in which a targeted U-boat was proceeding; and (b) they suffered time lags of collating and plotting or of decryption that allowed a U-boat Commander to nip out of the area where he had been tagged. What was needed, the RN decided early on, was shipborne HF/DF equipment that permitted immediate pursuit at sea of a close-by target.

The RN engineers realized the difficulty of reducing an installation to weight and size that would fit on a small escort vessel. So did the engineers of the German Navy, who particularly thought that the antenna required for HF/DF reception was far too large to be fitted to an escort vessel, such as a destroyer or frigate. Lacking apparently the imagination to conceive the impossible, Donitz’s technical advisors persisted in that view long after B-Dienst intelligence, visual observation, and U-boat experience had amply demonstrated otherwise, and, in fact, they remained obdurate on the point up to the end of the war, always explaining Allied detection successes as the work of radar.

The British resolved the weight and size problem in 1940, when they mounted a prototype FH 1 set and antenna on the destroyer HMS Hesperus in March of that year. Though the FH I’S performance was disappointing, the experiment proved that seaborne installations were possible. An improved FH 3 set, which gave an aural presentation of target data (requiring earphones) was fitted to two fleet destroyers, HMS Gurkha and Lance, in July 1941. And in October of the same year, an FH 4 set with visual presentation on a cathode ray tube, having met all test expectations, went into escort service on board the ex-American four-stack destroyer H.M.S. Leamington, which accompanied the troop convoy WS.107 to Madagascar in March 1942.

While a single HF/DF set could detect the azimuth bearing of a U-boat transmitting to base or to another boat on a high-frequency wave band, and even determine from the ground wave whether it was near or far (25–30 nautical miles being its maximum range), the crosscut bearing provided by a second HF/DF-equipped escort gave a fairly exact fix, and an escort could be detached to pursue the fix, attack the surfaced U-boat, drive it off, or force it to submerge, after which asdic would be employed. This action would have a particular value if the transmitting boat was a shadower, since underwater its observations and communications were greatly limited. Thus, seaborne detection made possible aggressive tactical operations that were not possible with shore-based detection. Too, HF/DF at sea provided data that even shipborne radar could not deliver, since HF/DF’s range was about 25 miles while Type 271 radar’s on a surfaced, trimmed-down U-boat was only 3,000–5,000 meters, depending on sea conditions. Production of HF/DF equipment was slow, however, owing to radar’s greater popularity as an “active” detection system. The number of sets at sea on RN and RCN escorts in 1942 was very small, but by spring 1943 at least two escorts with each convoy had either FH 3 or FH 4 equipment.

In the United States, production of a shipborne system called DAQ, based on the Busignies design, trailed the British work by many months. Though a USN decision was taken in March 1942 to build sets for ships, manufacturing delays prevented deployment until 1943. Even midway into that year, the first successful U.S. anti-U-boat attack mounted by an American HF/DF-equipped ship, the escort carrier USS Bogue (CVE-9), on 22 May 1943, was based on bearings taken by a British set just recently installed at Liverpool. The attack, made by Bogue’s TBF-1 Avenger aircraft, resulted in the surrender and scuttling of U-569 (Kptlt. Hans-Peter Hinsch). In his report on the action, Carrier Captain and Commander, Sixth Escort Group, Giles E. Short, U.S.N., stated:

“From the time the BOGUE left Belfast a continuous watch had been maintained on the newly installed HF/DF. Three radiomen from the BOGUE manned this equipment under the supervision of Sub-Lieutenant J. B. Elton, R.N.V.R., who had been assigned … to assist on this trip. The HF/DF equipment proved invaluable…. An HF/DF bearing was directly responsible for the attack on the sub-marine which surrendered…. Without doubt the … transmission at 1727Z was made by the U-Boat and wrote its death warrant.”

The second successful HF/DF-directed U.S. attack, by aircraft from the escort carrier USS Card, would not come until August 1943, well after the U-boat war had been decided. Meanwhile, from June 1942 through May 1943, British HF/DF-equipped escorts employed their new equipment with great effect, chasing down bearings unknowingly supplied by the loquacious German boats and attacking their surprised crews. Admiral Donitz was fully aware that the British were attempting to monitor his and the U-boats’ communications from shore-based stations, and though he was advised by Naval Staff engineers that no DF bearings of any accuracy could be acquired from high-frequency signals, he warily restricted radio use by his boats. For necessary traffic such as position updates, convoy sightings, and damage reports he had the engineers devise Kurzsignale (short signals), letter codes (by which, for example, a damage and position report could be made using only four letters of the alphabet), rapid frequency changes, and electronically compressed messages that went out in bursts, or “squirts.” These attempts to elude the shipborne HF/DF receivers generally failed, and the message content in its various forms was successfully unscrambled by the interception stations and GC&CS.

Prior to a convoy engagement, the attacking “wolfpack” patrol line normally observed radio silence, except that on some occasions (see the Fink line boats in chapters 4 and 5) the boats gave noon or evening position reports in great proliferation. Once the shadower boat reported a sighting, however, that boat’s signals to base became frequent; and with the battle joined, other boats soon joined in the chatter: When on 4–9 February 1943 U-boat Groups Landsknecht and Haudegen attacked Convoy SC.118, the U-boats made 108 radio transmissions in a period of seventy-two hours, and one boat alone, U–402, sent forty-one signals during the four-day battle, all of which were detected by shipborne HF/DF.

Although Dönitz was prepared to take some risks of DF detection with his high-volume command and control communications net, he never realized during the war how thoroughly his boats at sea were being exposed by that system; just as, of course, he never knew that his own “rudder commands from the beach” were being read by GC&.CS and Rodger Winn. Because it brilliantly exploited the German reliance on radio control, Britain’s mostly unheralded shipborne HF/DF deserves to be recognized as one of the principal tools employed by the Allies against the U-boats up to May 1943—hence its extended treatment here—and it would play a particularly significant role in the two May battles for transatlantic Convoys ONS.5 and SC.130 (described in chapters 4, 5, 6, 7, and 10).

During the crossing of convoy ONS.5 in May 1943 , Royal Navy destroyer HMS Duncan (Senior Officer Escort Group B7, Commander Peter Gretton), which was equipped with FH 4, counted 107 DF contacts on U-boats before having to leave the convoy because of fuel depletion. The frigate HMS Tay, equipped with FH 3, counted 135 transmission intercepts, many of them shared as cross-cuts with HMS Duncan before 3 May, when the latter withdrew. The same two escorts, again under Gretton, accompanied SC.130 later in the month, when the surface escorts had excellent air cover, and collected 104 DF bearings between them. Later, Gretton described how Duncan and Tay were “able to get fixes on U-boats transmitting near us with great accuracy and to send aircraft quickly after them.” In his analysis of the battle from the other side of the hill, Admiral Dönitz, of course, attributed the British success to radar:

“These attacks could only be attributed to a very good radar location device which enables the aircraft to detect the boat above the clouds even, and then to make a surprise attack from the clouds. The amazing thing is that apparently at the time only 1 to 2 machines [aircraft] in all were escorting the convoy, according to intercept messages of aircraft operating. Each machine, however, detected during the whole day one boat more frequently than every quarter-hour, from which it must be concluded that the enemy’s radar hardly missed a boat.”

German historian Jürgen Rohwer has concluded: “If we analyze the great convoy battles between June 1942 and May 1943 … the remarkable fact is that the outcome of the operation always depended decisively on the efficient use of HF/DF.” Although effective use of radar detection by escort ships and aircraft was also progressing from strength to strength during that same period, and while granting that it was the new shipborne centimetric radar operated by the escorts of ONS.5 on the fogbound night of 5/6 May 1943 that made possible that most pivotal Allied victory in the U-boat war (chapters 6 and 7), still, in normal visibility conditions, more U-boats in the convoy battles of 1942–1943 were first detected by HF/DF than were by radar.


HF/DF High Frequency Direction Finder in museum ship HMS Belfast


HF/DF antenna

What the British at this time called RDF (for Radio Direction Finding, which was a deliberate cover) and what the Americans called Radar (for Radio Detection And. Ranging), an acronym coined by USN Lieutenant Commanders Samuel M. Tucker and F. R. Furth, is an electronic tool understandable to modern readers familiar with its use in air traffic control, weather forecasting, and police speed guns. Instead of passively receiving radio signals, as in HF/DF, a radar set actively generates a stream of short radio energy pulses that, once transmitted through an antenna, return echoes from any physical objects the stream encounters—objects as solid as an airplane and as gossamer as a cloud. The presence of these objects is displayed on a cathode ray tube (CRT) in such a way that the radar operator can determine mass, bearing, and range.

The technology was co-invented in 1934–35 by the British (Scottishborn) engineer Robert Watson Watt, superintendent of the Radio Department of the National Physical Laboratory near the Berkshire town of Slough, and by American engineers, notably Robert Morris Page, Albert Taylor, and Leo Young, at the Naval Research Laboratory at Anacostia in Washington, D.C. Thanks to the original research of Watson Watt, who is customarily called the “father” of radar, British engineers were able to erect the famous Chain Home radar network that, by providing range, course, and altitude of incoming Luftwaffe bombers and fighters, helped the RAF to win the Battle of Britain in 1940.

Quickly miniaturized, RDF sets were installed in RN escort vessels beginning in fall 1940. This first equipment, Type 286 (1.5 meter wavelength), could obtain echoes on a trimmed-down U-boat at no more than 1,000 meters; hence, except in moonless nights or in fog, it was frequently outperformed by a human lookout. By March 1941 about ninety escorts were so equipped. In the same month and year Type 271 (10-centimeter, or S-band) radar was fitted to an escort, the corvette H.M.S. Orchis. When 271 entered general service with the escort fleet in 1941–42, U-boat detection range jumped to 3,000–5,000 meters. By May 1942, 271 was mounted on 236 RN ships of all categories.

The 271 was made possible by a remarkable device called the resonant multi-cavity magnetron valve. The invention of two British physicists at the University of Birmingham, John Randall and Henry Boot, the cavity magnetron’s central feature was a cathode and anode structure built into a block of copper through which either six or eight symmetrical holes were bored. The high-frequency radio oscillations produced by the device enabled a radar apparatus to operate on a wavelength of 9.7 centimeters—rounded out in popular usage to “10-centimeter,” or “centimetric” radar.42 This represented an extraordinary advance in power, range, and accuracy over the previous “metric” radar, and constituted, in the words of Britain’s most accomplished air and naval operations research scientist, physicist Patrick M. S. Blackett, “one of the most decisive technical developments made during the war.”

Its narrow horizontal beam width enabled a single escort to find, fix, and hold a nearby U-boat on the surface at night and in fog. And from its first operational use until the fall of 1943, its beam was not detectable by any German search receiver then at sea. A U-boat Commander proceeding on the surface at night near a convoy escort had no way of knowing that he was being “painted.” But in the plot, or operations room, of the nearby escort, that U-boat was exposed starkly on the 271’s plan position indicator (PPI), where a sweeping radial line from the center of the circular CRT screen rotated in synchronization with an outside antenna and, each time it passed the U-boat’s position, displayed it as a bright phosphorus-lit spot.

In September 1940, a seven-member British Technical and Scientific Mission to the United States, headed by physicist Henry Tizard, arrived in Washington, D.C., with a black solicitor’s box containing, among other scientific objects and blueprints, a hand-sized eight-cavity magnetron. The gift was not entirely magnanimous: the British knew that to win their war they would need American technological assistance and industrial capacity. Members of Tizard’s mission, which was conducted at the height of the Battle of Britain, were mindful, too, that their homeland might soon be invaded; if the war was lost in the Old World, this means for continuing the fight would be in the hands of the New.

Grateful U.S. radar specialists acknowledged that the gift put them two years ahead of the curve, and James Phinney Baxter III, official historian of the U.S. Office of Scientific Research and Development, was moved to write in 1947, “When the members of the Tizard Mission brought [a cavity magnetron] to America in 1940, they carried the most valuable cargo ever brought to our shores.” The encomium should not be accepted uncritically to mean that centimetric radar alone, or even principally, won the war at sea. By itself it was not a war winner, though one could certainly say it was a battle winner, as in the final stage of the surface battle for Convoy ONS.5 (chapter 7), where centimetric radar was the triumphant technology. In the regular structure of surface engagements between escort vessels and U-boats, centimetric radar fell into place as one of five technological innovations that, taken together, swept the field. The first four were, in the order in which they were employed: (1) HF/DF; (2) radar; (3) hydrophone effect (using asdic to listen for underwater noise such as cavitation from a U-boat’s propellers); and (4) asdic echo contact. (Close in, one must not discount the Mark I eyeball.) The fifth innovation was TBS (Talk Between Ships), an American-developed very high frequency (VHF) voice radio-telephone (R/T) system, introduced in early 1941 and universally fitted on escorts a year later. At low power and short range it was immune to DFing. TBS enabled an escort commander to give instantaneous direction to the movement of his ships and to converse with overhead air cover. It also enabled the individual surface escorts to coordinate attack maneuvers between and among themselves. It is clear that by the date of the May 1943 battles, an Atlantic escort was an electronics platform of daunting authority.

RAF Coastal Command began the war with a fleet of Avro Ansons (301), Lockheed Hudsons (53), Vickers Vildebeests (30), Short Sunderlands (27), Saro Londons (17), and Supermarine Stranraers (9). The most numerous aircraft, the Anson “Annies,” which entered RAF service in 1936, were obsolescent, and by the close of 1941 had been replaced by Wellingtons, Halifaxes, Whitneys, and other advanced designs; so, too, the Vildebeests, Londons, and Stranraers were struck off the inventory. The Hudsons, an American passenger plane refitted as a bomber, continued to be purchased and used in large numbers.

But the principal survivors among the original list, which in fact soldiered on to the end of the war, were the Sunderland flying boats. Admirably equipped for long-range anti-submarine patrols, the “Queens,” as air crews called them (U-boat crews, noting their languorous flight maneuvers, called them mtide Bienen, “tired bees”), would score the second-highest U-boat tally of the war. Third in ranking would be the Vickers Wellington, a two-engine bomber never designed for maritime operations, but greatly effective in the Bay of Biscay (see chapter 8). Two American designs that came on the scene in 1941 and performed well were the Boeing B-17 Flying Fortress, a four-engine heavy bomber, and the Consolidated PBY-5 and PBY-5A (amphibian) Catalina twin-engine flying boat.

Short Sunderlamd Flying Boat

Short Sunderland Flying Boat

The overall favorite aircraft in RAF Coastal Command and the most successful sighter and destroyer of U-boats was the four-engine Consolidated B—24 Liberator heavy bomber. Though somewhat harder to handle, more demanding in maintenance time, and certainly more drafty than the Fortress, the Liberator was esteemed for its range. In a V.L.R. (for Very Long Range) modification, where weight reduction was achieved by removing self-sealing liners (if present) to the fuel tanks, most of the protective armor plating, the turbo-superchargers, and the belly gun turret, the Liberator had a low-altitude operational range of 2,300 nautical miles at an economical 150 knots, while carrying, on takeoff, 2,000 gallons of high-octane fuel and eight 250-pound depth charges (gravity bombs with hydrostatic fuses). This was the aircraft that would give overhead coverage to threatened convoys in distant midocean lanes, force shadowing U-boats to submerge (which until May 1943 they uniformly did on sighting a reconnaissance bomber), and thus retard their speed, maneuverability and visibility, hence, their potential for organizing packs. This was the aircraft that, operating from both shores of the Atlantic, would eventually plug the Air Gap between Iceland and Newfoundland in May 1943—assisted by newly introduced carrier-borne aircraft.

No. 120 Squadron received the first Mark I Liberators in June 1941 and in September began flying nine of them southwestward from bases in Northern Ireland and Iceland to their Prudent Limit of Endurance (PLE), governed by fuel remaining. But the numbers of these aircraft in Coastal remained depressingly few, as American Admiral Ernest J. King, Commander in Chief, United States Navy (after 30 December 1941), hoarded most Navy-assigned Liberators (designated PB4Y-1) for the Pacific theater, while almost all of the RAF-assigned Liberators that made it to the U.K. were claimed by Bomber Command. By September 1942 Coastal still had only one squadron (No. 120) containing V.L.R. Mark Is, six in number. The V.L.R.s were “being allowed to die out,” Coastal complained to the Under-Secretary for Air. The squadron list also included two Mark IIs (range 1,800 miles) and three Mark Ills (1,680 miles). Other squadrons had PBY-5 Catalinas (1,840 miles) and PBY-5AS (1,600 miles), but the V.L.R. was the most desperately needed long-distance performer. (There were none in Newfoundland, Canada, Gibraltar, or West Africa.) And Coastal’s Atlantic operations were being denuded of other essential resources, including, between October 1941 and January 1942, 166 air crews and whole squadrons of Catalinas shipped to overseas bases.

B-24 Liberator bomber

B-24 Liberator bomber

Penetration by GC&;CS of the German naval cipher and the development of a fairly accurate plot in the OIC Tracking Room made it possible, on 9 May 1941, for the Admiralty to draw a distinction between threatened and nonthreatened convoys. Coastal thereafter concentrated its forces on threatened convoys, thus making more efficient use of its air assets, but without V.L.R. aircraft, sorties directed to threatened convoys outside a radius of 450 miles from air bases could not be sustained beyond a short period of time, and Coastal began to worry about “the lavish expenditure of engine hours in order to get, at most, two or three hours with the [threatened] convoy.”

Even on as late a date as February 1943, when Air Marshal Sir John Slessor took over as Air Officer Commanding-in-Chief (AOC-in-C), Coastal Command, No. 120 still remained the lone operating V.L.R. squadron. Based at Aldergrove in Northern Ireland with a detachment at Reykjavik, Iceland, it then counted among its assets five Mark Is and twelve Mark IIIAs modified to V.L.R. requirements. A new squadron with modified Mark IIIAs was forming at Thorney Island, near the Isle of Wight on the southern coast of England, but it was not yet operational; neither was No. 502 at nearby Holmsley South, which was awaiting V.L.R.-modified Halifax lIs. And still, by Admiral King’s decision, there were no Liberators in Newfoundland. When Convoys SC.122/HX.229 were pummeled in the following month in March 1943 , President Franklin D. Roosevelt pointedly asked King where all the Navy Liberators had been.

That more of the Liberators then in the U.K. had not been allotted to ASW work was owed to the fixation of RAF Air Staff (abetted by Churchill) on night bombing of Germany. Contention between RAF Coastal and Bomber Commands over the question of which targets, U-boats or factories, would more effectively create a matériel advantage for the Allies’ cross-Channel invasion of the Continent simmered all through the first six months of 1943. The doctrinal dispute, which, particularly in March of that year, involved heavy-handed wrestling over bomber allotments, extended to the question, Was the U-boat force better destroyed at sea (Coastal) or at its construction and assembly yards (Bomber)?

Historians who incline to the Coastal position in that debate can only wonder how much earlier and more thoroughly the U-boat threat might have been brought to an end had the majority of V.L.R. Liberators not been concentrated on land warfare, where postwar analysis showed that overall German war production had not been substantially reduced by Allied bombing and that “de-housed” civilians—a Bomber Command term—had not faltered in morale. In a recent book, Clay Blair writes: “A number of studies would show that a Coastal Command ASW force of merely a hundred B-24S could well have decisively crushed the U-boat peril in the summer of 1941, sparing the Allies the terrible shipping losses in the years ahead.” That might be pitching it a little high, since the essential improvements in attack procedures described in the following chapter were not all in place during 1941, but the point is well taken.

A smaller number than a hundred V.L.R. bombers is proposed as sufficient in 1942–1943, when Coastal Command attacks were far more lethal than before, by a historian of the maritime air war, Alfred Price. He holds that three squadrons, comprising about forty aircraft, “would have gone—and later did go—a considerable way towards nullifying the threat to convoys in mid-Atlantic.” And the transfer of that number to Coastal from RAF Bomber Command would not have appreciably weakened the bombing offensive over Germany. After all, Price points out, many times Bomber Command was losing that number of bombers in a single night.

By the end of 1942 none of RAF Coastal Command aircraft was equipped with centimetric radar. Not until February 1943, after resolution of numerous technical problems and intense competition between Coastal and Bomber Command for the equipment, was the Telecommunications Research Establishment (T.R.E.), of the Ministry of Aircraft Production, at Malvern in Hereford and Worcester (after May 1942), able to fit ASV (Air to Surface Vessel) Mark III 10-centimeter radar to Coastal Liberators, Wellingtons, Sunderlands, and other reconnaissance bombers. In the meantime, since 1940, Coastal aircraft operated with metric (1.5 meter) ASV Mark II equipment, which was unsatisfactory for several reasons: limited range, approximately 10 miles maximum; unclear returns because of sea clutter; a hard-to-read light-bar graph display; poor construction resulting in numerous failures and difficult servicing; chronic shortage of parts; and poor training of operators.

When in December 1941 RAF Coastal Command Headquarters at Northwood in Middlesex reflected on the maritime air war to date, it could count fewer than a handful of kills and one capture, most of them shared with surface vessels. A force that was projected from the outset to have an offensive, not defensive, purpose, as yet Coastal Command was not meeting its mark. At fault was not a lack of commitment. Coastal Command had responsibilities other than the anti-submarine war, for example, protection of the United Kingdom’s coastal waters and destruction of enemy shipping, but by 1941 its main effort was clearly directed at the U-boats. Kills had not materialized in the expected number because of aircraft shortages, particularly in the long-range category, inadequate search tactics, poorly executed attack procedures, and the above-mentioned radar deficiencies, but since May 1941 Coastal air was performing at least one indisputable service by concentrating “scarecrow” patrols over threatened convoys, while leaving unthreatened convoys on their own.

Aircraft shortages would be made up gradually as Prime Minister Churchill’s cabinet became more attuned to the gravity of the Atlantic struggle, Churchill saying that what was most needed were new air tactics and time to train. The latter would be provided by a totally unexpected coup de main that led to a diminution of U-boat operations in the convoy lanes. The former would be provided not, as might be expected, by an increase in hardware, by astute command judgment and leadership, or even by air crew proficiency and gallantry, though each of these factors was an essential precondition. The improvement would come from a band of civilian physicists, mathematicians, and other academics, “Boffins” as they came to be called—“gentlemen in grey flannel bags”—who took on a myriad of complex search and attack problems and, to the astonishment of the uniformed service, solved them. But first, the events of 7 December 1941 and following.



To Defend or to Hunt?

Probably the anti-submarine campaign in 1943 was waged under closer scientific control than any other campaign in the history of the British Armed Forces. PROFESSOR PATRICK M. S. BLACKETT

Gaily the backroom boysPeddling their gruesome toys, Come in and make a noise, Oozing with science! Humbly their aid we’ve sought; Without them we’re as nought, For modern wars are fought By such alliance. ANTI-SUBMARINE WARFARE DIVISION NAVAL STAFF, ADMIRALTY

The defeat of the U-boat must remain a first charge on the resources of the United Nations

THE JAPANESE ATTACK ON Pearl Harbor caught Hitler and Donitz just as much by surprise as it did the Americans. Dönitz reacted swiftly when on 9 December Hitler lifted all previous restrictions on attacks against both USN warships and merchant vessels under U.S. flag. His Commanders had long bridled under those restrictions, since U.S. destroyers had been escorting Britain-bound convoys as far as Iceland, and it seemed to Dönitz that the Americans had long been belligerents in everything but name. Not surprisingly, there had been several incidents involving U-boats and USN vessels, including the sinking of the destroyer U.S.S. Reuben James by U-552 (Kptlt. Erich Topp) on 31 October 1941. Unknown to Dönitz, another Admiral, Ernest J. King, then Commander in Chief Atlantic Fleet (CINC-LANT), was also itching to shake off the fetters of formal nonbelligerency.

When war between the two nations came formally on 11 December, King pulled all his destroyers home to the U.S. Atlantic seaboard expressly to defend it against the U-boats, stating that, “The imminent probability of submarine attack in that area, and the weakness of our coastal defense force, make it essential that the maximum practicable number of our destroyers be based at home bases.” The move seemed all the more sensible since U-boat activity had slackened in the east-west convoy lanes, Dönitz having been compelled by the Naval Staff in Berlin to withdraw boats from those waters for stations off Gibraltar to attack Mediterranean-bound supply transports during the British winter offensive against General Erwin Rommel’s Afrika-Korps.

Dönitz was pleased to meet King’s expectations. He immediately requested that twelve boats be made available for an operation along the North American coast, but Naval Staff allowed him only six, of which one, the newly commissioned U-128, had to be withdrawn because of mechanical problems. The other five were U—123, Type IXB (Kptlt. Reinhard Hardegen), U-125, IXB (Kptlt. Ulrich Folkers), and U-66, IXC (Korv. Kapt. Richard Zapp), which were to form Gruppe Hardegen for attacks in U.S. waters; and U-109, IXB (Kptlt. Heinrich Bleichrodt) and U-130, IXC (Korv. Kapt. Ernst Kals), which were to form Gruppe Bleichrodt for attacks southeast of Halifax and in Cabot Strait off Cape Breton Island. To their joint operation Dönitz gave the code-name Paukenschlag—“beat on a kettledrum”—or “Drumbeat.” What was meant here was not “drumroll,” as some would have it, but a single percussion of a timpani stick on the stretched head of a brass-barreled kettledrum; a sudden blow—einen kräftigen Paukenschlag— since, as Hardegen, Commander of U—123, insisted to the writer, the aim was to deliver a simultaneous surprise attack on a given day, later signaled to be 13 January. Though many waves of additional U-boats were to follow the first five to North America, their latter operations were not called Paukenschlag. None of the original five boats would make their assigned positions by the 13th, but, two days before the deadline, U-123 sank the 9,076-GRT British freighter Cyclops 300 miles east of Cape Cod, effectively beginning the campaign.

News of the Drumbeat fleet’s coming was flashed by Rodger Winn in O.I.C at Royal Navy Western Approaches in UK to the U.S. Navy Department (Main Navy) in Washington, D.C. From there the Tracking Room’s U-boat position estimates were sent, day by day, to the appropriate USN eastern seaboard defense commands. The sinking of Cyclops on the 11th January was all the confirmation anyone required. But Hardegen gave further notice of his coming, sinking the 9,577-GRT former Norwegian motor tanker Norness 60 miles southeast of Montauk Point, Long Island, on the night of the 14th.

Twenty-one of the destroyers Admiral King had brought home to defend U.S. coastal waters were stationed at ports that bracketed Hardegen’s approach, from Casco Bay, Maine, in the north to Norfolk, Virginia, in the south. All were battle-ready. Four other destroyers in the same districts were ready “only in an emergency.” But no emergency was declared. Nor were the ready-category destroyers deployed by Admiral King or anyone else to meet the invasion. By this date, effective 30 December 1941, King was Commander-in-Chief, United States Fleet (COMINCH), with headquarters at Main Navy, but he maintained direct personal command over all anti-submarine warfare (ASW), requiring the various Atlantic commands in the U.S. Strategic Area to clear all such operations through him.

As it happened, by King’s order or compliance, most of the destroyers that he had assembled on the seaboard to defend against “submarine attack in that area” were sent off or held in port for other missions instead. Even when, at 10:00 P.M. Eastern Time on the 15th, Hardegen stood at the Ambrose Channel Lightship station marking the entrance to New York Harbor (which he had reached in 22 days of transit, 98 percent of the distance on the surface), with the tip of Sandy Hook, New Jersey, to his port and Coney Island to starboard, none of the seven ready-status destroyers in the harbor that night—U.S.S. Gwin, USS Mayrant, USS Monssen, USS Rowan, USS Trippe, USS Roe, and USS Wainwright—sallied forth to meet him. Hardegen then leisurely withdrew and sank the 6,800-GRT British tanker Goimbra on his way out of the harbor approaches. The worst was yet to come.

For three weeks Hardegen and the other two boats in his group savaged Allied independently routed shipping along the East Coast as far south as Cape Hatteras and into the deeper waters of the U.S. Strategic Area. They were joined there eventually by the two Gruppe Bleichrodt boats, which, harried by Canadian destroyers and aircraft and impeded by freezing weather, made revolutions south to friendlier U.S. waters where coastwise shipping was steaming without surface or air escort, advancing along the buoys in straight line ahead, as though in peacetime, and mercilessly outlined by shore lights. Not only were buoy lights and lighthouses undimmed, but coastal communities, amusement parks, and beach resorts were still brilliantly lit, providing a luminous backdrop to merchant ship silhouettes as they passed north and south.

This was particularly true along the Jersey shore, where even the headlights of automobiles could be seen from U-boat bridges. Commanders learned that they could save fuel by bottoming out during the daytime, and then surfacing at night to wait in stationary bow attack position, like Prussian deer hunters in camp chairs waiting for game to be driven in front of their guns. And there was little in the way of defenses to concern them. An occasional destroyer or aircraft would be sighted, and at dusk on the 15th one aircraft chanced across U—123’s course and dropped four bombs to starboard, but continued without circling or returning. Neither the USN nor the U.S. Army Air Corps made a single planned attack or a “scarecrow” effort to keep the U-boats down.

At Kernevel, Admiral Donitz was enthusiastic about the early reports, which showed, he said, “that activities of U-boats can be successful much longer than was expected.” Though it was being waged at a great distance, the tonnage battle remained the same battle. Only the venue had changed. The transportation of the sinews of war was an endless chain, whether in the Western Approaches to Britain, or in midocean, or off the Carolina Capes. The chain could be pulled apart at any point. It was immaterial where. And now, the most vulnerable link of it—Donitz’s new Schwerpunkt (focus)—was the American coast.

Altogether, the five Paukenschlag boats sank twenty-five ships for a total tonnage of 156,939 GRT, a number that compares favorably with the 152,000 GRT sunk by nine boats in the famous “Night of the Long Knives” in October 1940. While the simultaneously delivered drumbeatlike strike that Donitz had envisioned did not happen as scheduled, the operation was a triumph nonetheless, and in the weeks and months that followed, an exultant Dönitz sent out wave after wave of additional Type IX boats to pursue the advantage. The first blood drawn by Drumbeat soon became a hemorrhage, staining the waters off Florida, in the Gulf of Mexico, and throughout the USN-protected Caribbean basin, including the Panama Sea Frontier. Not only American flag ships but scores of British bottoms sank beneath the torpedo onslaught.

Complained Royal Navy Commander-in-Chief Western Approaches Admiral Sir Percy L. H. Noble: “The Western Approaches Command finds itself in the position today [8 March] of escorting convoys safely over to American eastern seaboard, and then … finding that many of the ships thus escorted are easy prey to the U-boats … off the American coast or in the Caribbean.” Even some Type VIIC boats, by filling their torpedo compensating tanks and freshwater tank with fuel oil, managed to make the voyage over (and back) to participate in the “Second Happy Time.” A new set of U-boat “aces” emerged, including Hardegen (U-123), Kptlt. Johann Mohr (U-124), Kptlt. Erich Topp (U-552), Kptlt. Rolf Mützelburg (U-203), and Oblt.z.S. Georg Lassen (U-160).

Beginning in April, boats operating in the Gulf and Caribbean were able to extend their time on station thanks to the deployment of a new large (1,688 tons surface displacement) U-boat type, the XIV, which carried no torpedoes but, instead, 700 tons of oil as well as spare parts, ammunition, food, other supplies, a physician, and replacement specialist ratings. Popularly called Milchkuh (milch cow), the U-tanker’s capacity to refuel and revictual extended the patrol time of a Type IX boat by eight weeks, that of a Type VII by four, thus becoming for Donitz a long-distance force-multiplier. The U-459 (Kptlt. Graf Georg von Wilamowitz-Moellendorf) was first on station, refueling the IXB U-108 (Kptlt. Klaus Scholtz) on 20 April, and then fourteen more boats in April and May. By the beginning of summer three more milch cows were tending pump at assigned naval square positions in the Western Atlantic.7 (By the end of summer the British would have to contend with their ministrations in the transatlantic lanes, particularly in the Greenland Air Gap.)

As the number of ships sunk mounted into the hundreds, King’s Navy came under heavy pressure from various quarters to do something about shore lighting and to institute coastwise convoys. In March, a month when oil tankers went down at an average of more than one a day, the Petroleum Industry War Council persuaded the Navy and War departments, which to that date had shared responsibility for coastal lights, to suppress them. The two departments formally agreed that thenceforth control of coastal lights would be “a Navy function.” Admiral King quickly exercised his sole authority, ordering that, despite the understandable protests of amusement parks, resorts, and other business interests, all shore lights must be “dimmed”—blackouts, he said, “were not considered necessary.” Although both the German and British coasts practiced total light elimination, dim-out was as far as King would ever go during the war. Tragically for the freighter and tanker crews, U-boat Commanders were able to silhouette shipping traffic about as well under dim-out regulation as under full illumination, especially in conditions of haze and low-lying cloud banks.

As for convoy, King would have none of it, arguing that he did not have sufficient escort vessels to make convoying possible and safe. When King thought of escorts he thought of destroyers, and with most of that class ship needed either in transatlantic work or in the Pacific (always King’s overriding concern), he considered ships of lesser draft and tonnage as useless for escort. “Stout hearts in little boats,” he said, “cannot handle an opponent as tough as the submarine”11—this in spite of the fact that the British had been doing quite well with 205–208-foot “Flower” class corvettes; and in spite of the fact that later, in May and June, 165-foot Coast Guard cutters, USCG Icarus and USCG Thetis, sank two of the first three U-boats destroyed in U.S. waters. King’s doctrine became: “Inadequately escorted convoys are worse than none.” This was the exact opposite of all that British experience had taught since 1939, and, indeed, since 1917, when the Royal Navy of World War I learned the value of convoy under USN tutelage.

Gradually, however, King was forced to change his mind, not least because of the remonstrations of Rodger Winn, who, though a lowly Commander and a reservist at that, was dispatched to Washington by an exasperated Admiralty to reason with the obdurate USN chief.’ By mid-March it was clear that King was undergoing a mind-change. The “little boats” he had disparaged before he now began assembling for convoy escort duty: 173-foot-class patrol craft, 165-foot-class cutters, 147-to-162-foot RN trawlers on loan from the Admiralty, no-foot-class subchasers, down to 83-foot-class cutters, which, though originally considered “of very limited usefulness,” proved, once convoy was instituted, to be an effective guard on the short-leg run between New York and Delaware Bay.

With these and other small craft, joined by nine destroyers, King and his subordinates sailed the first southbound convoy, KS.500, from Hampton Roads on 14 May; and a northbound formation, KN.100, steamed out of Key West the next day. Later in May, links were established to New York and Halifax; and in August-September a Galveston-Mississippi-Key West link gave protection to tanker traffic out of Texas ports. The Caribbean basin was last to come into the convoy system.

In U.S. East Coast waters the good effects of convoy practice were almost immediately apparent. Whereas in the U.S. Strategic Area between the latitudes of West Quoddy Head, Maine, and Jacksonville, Florida, there had been forty-two sinkings in March and twenty-three in April, the number fell to four in May, rose to thirteen in June, fell to three in July, and then to zero for the remainder of the year. Figures for sinkings around the Florida peninsula showed a similar decline, as the Gulf figures would, too, after convoy became the routine mode of traffic there in late summer. As a result, Admiral King began saying, on 21 June: “Escort is not just one way of handling the submarine menace; it is the only way that gives any promise of success.”

As another result, in July, King’s counterpart Admiral Dönitz transferred the main U-boat effort back to wolfpack tactics in the transatlantic sea lanes. He had known that it would be only a matter of time before his independently operating boats would have to give up the American coast, but he had never imagined that the shooting season would last as long as it did: six months, if one reckons it from U—123’s sinking of Cyclops on 13 January to mid-July, when the U-boat withdrawal began. Left behind on the seabeds from Maine to Galveston to Panama were the hulks of 397 Allied ships and the bones of no fewer than 5,000 souls—U.S., British, Norwegian, and other merchant seamen; USN and RN officers and men; and civilian passengers. The human casualties were twice those suffered at Pearl Harbor. Many other ships, not sunk, were damaged, some with death and injury resulting.

Overall, the six-months-long entombment of ships and men constituted one of the greatest maritime calamities in history. In terms of ships, raw resources, and matériel, it was the American nation’s costliest defeat of the war. On 19 June 1942 U.S. Army Chief of Staff General George C. Marshall lamented: “The losses by submarines off our Atlantic seaboard and in the Caribbean now threaten our entire war effort.” For the Germans the operation on the American littoral was the most successful sustained U-boat campaign in the whole course of the war. In exchange for negligible losses—nine U-boats sunk—the U-Bootwaffe carried off a triumph that was fully the equivalent of victory in a major battle on land. One must agree with historian Gerhard L. Weinberg that the offshore battle also “must be regarded as the most disastrous defeat ever suffered by American naval power"


The U.S. Navy might well be grateful that it was not worse than it was, which one may assume it would have been if Donitz had been allotted the twelve boats he sought for the opening blow; and had Hitler not in February diverted twenty operational boats to reconnaissance duty off the coast of Norway, where he expected imminent British landings; and had not a particularly severe European winter frozen the Southern Baltic parts where scores of new boats were trapped while working up;’ and had not thirteen boats, including the now much-sought-after Type IXs, been lost in the ill-starred attempt to stop North Africa-bound convoys in the vicinity of Gibraltar.

If there were any consolations that the Allies could draw from the massacre on the American Main, it would seem that they were three in number: First, it occurred at just the time when the new Kriegsmarine four-rotor cipher Triton came into service fleet-wide, and as a result, except for three days, 23 and 24 February and 14 March, GC&CS went blind for eleven months. For the Allies to possess Enigma information during the period February-July would have granted them no special advantage, since the majority of U-boats, operating independently and transmitting infrequently, could not have been located regularly by cryptographic intelligence; nor could shipping have been diverted around them on the strength of Sigint. Of course, when the U-boat offensive returned to midocean convoy routes starting in August, and radio-directed patrol lines began forming again, the absence of Enigma was keenly felt.

Even then, Commander Winn’s Tracking Room was not without resources, which included access to the Heimische Gewässer (Home Waters) key, which continued to be used by the Kriegsmarine for Räumboot (motor minesweeper) escorts that shepherded U-boats in and out of the Biscay bases; penetration of the Tetis key used by new boats working up in the Baltic; RFP, or radio fingerprinting, which could identify an individual U-boat’s transmitter; TINA, an oscillographic operator signature device that displayed the specific keying style, or “fist,” of each U-boat Morse sender; HF/DF; and knowledge long assembled in the Tracking Room about BdU’s operating theory, characteristics of particular Commanders, U-boat routes, average speed of advance, and endurance at sea. From these remaining sources, plus Winn’s canny intuition, the Tracking Room developed daily an estimate, or “working fiction,” of U-boat operations.

The second consolation, to British strategists as much as to any like-minded officers in the USN, was the convincing demonstration in American waters of the value of convoy as a battle-winning expedient. And why was it so? Because either (I) the convoy drew U-boats to warships: instead of fruitlessly searching for the elusive craft—“hunting the hornets all over the farm”—the escorts had the U-boats in close proximity, where they could be attacked; or (2) the U-boats, unnerved by the hazards of attacking protected shipping, withdrew to more congenial waters, as happened in the American experience; or (3) attack opportunities declined mathematically, since if a U-boat was not correctly positioned to attack a convoy, it missed all the ships that formed it, and had to wait a long while for another chance.

The third consolation that the Allies could take from the first half of 1942 was that the sea war in the west bought time for RAF Coastal Command and RN escorts to enlarge forces, improve training, and perfect tactics. It is to that opportunity, and to the role of the boffins, that our narrative now turns.

When in June 1941 Air Marshal Philip Joubert de la Ferté took command at Northwood, succeeding Air Chief Marshal Frederick Bowhill as Air Officer Commanding in Chief (AOC-in-C) RAF Coastal Command, he decided that he needed an advisor at his elbow in the operations room who was not a member of the uniformed service: a civilian scientist, privy to every operation and every command secret, who could give him objective, disinterested guidance on the day-by-day anti-U-boat war. In Joubert’s radical concept this civilian would advise on matters normally understood as being exclusively within the province of the RAF officer. His choice fell on Patrick M. S. Blackett, one of the most accomplished and versatile physicists of his day— “wonderfully intelligent, charming, fun to be with, dignified and handsome … married to one of the most delightful women in the world who did much to prevent him from becoming too serious.” An Royal Navy veteran of World War I, Blackett had given scientific advice to the Air Ministry during the mid-1930s when serving as a member of the shortlived “Tizard Committee,” chaired by physicist Henry Tizard. Other members of that body, which was largely responsible for the initiation of Britain’s radar network, were physiologist A. V. Hill and physicists H. E. Wimperis, A. P. Rowe, and F. A. Lindemann, later Lord Cherwell. This was a prototype “Operational Research Section,” a term that radar pioneer Watson Watt would later claim to have coined in 1940.

With Lindemann, whose presence on the Tizard committee was owed to pressure exerted by the then Mr. Winston Churchill, Blackett had a difficult relationship up to and throughout the war. In 1939–1940 Blackett worked with the Royal Aircraft Establishment (R.A.E.) at Farnborough, where he designed bombsights and other equipment that he personally flight-tested. With physicist Evan James Williams (1903–1945), whom he recruited to Farnborough, he worked on magnetic field detection of submarines. Blackett served seven months in 1940–1941 at the Anti-Aircraft (A.A.) Command at Stanmore, where he worked on gun-laying radar sets, until March 1941, when he received the call from Joubert.


Professor Patrick Blackett , later honored as Baron Blackett for his wartime services to Crown

Taking Williams with him, Blackett made it clear to Joubert that he had severed all connections to the design, manufacture, and testing of weapons. “From the first,” he wrote later, “I refused to be drawn into technical midwifery.” Instead, he would hold himself free for nonroutine investigations of a purely scientific nature; he would encourage numerical thinking on the conduct of operations; he would subject every assumption to quantitative analysis and empirical test; and thus he would “help to avoid running the war on gusts of emotion.” He rejected, too, the constant clamor of all the services for “new weapons for old.” What was needed at Coastal, he concluded, was for commanders, air crews, and maintenance personnel to make “proper use of what we have got.”

To that end he and Williams began scrutinizing every aspect of Coastal’s operations and asking or recognizing the importance of questions about even the blindingly obvious. To give an example: There had to be measurable explanations for what was then Coastal’s very low U-boat sighting rate and mere 1 percent kill rate of those boats sighted. A month after assuming his new position, Blackett paid a visit to Admiral Percy Noble’s Royal Navy Western Approaches operations room at Derby House, Liverpool, from which all British surface and air escorts were controlled; indeed, it should be pointed out that since March 1941, Coastal, while remaining an essential arm of the RAF, had been under the operational command of the Admiralty, the two services sharing responsibility for the air war against U-boats. The positions of escorts as well as the estimated positions of U-boats were displayed on an immense wall plot. A quick glance at Coastal Command aircraft positions and examination of their numbers of hours flown led Blackett to calculate on the back of an envelope the number of U-boats that should be sighted by the aircraft. Back at Northwood he checked actual sightings for that day and found them to be four times fewer than what he had calculated.

The reason eluded him until one day a Wing Commander asked casually, “What color are our aircraft?” Blackett recognized at once that that was the right question. RAF Coastal Command bombers, designed originally for night action over land, were painted black—a paint that made them stand out starkly against a North Atlantic cerulean blue or overcast sky, thus enabling an observant U-boat to dive before being sighted. Using first models and then aircraft, Blackett found that a white-painted bomber was sighted at 20 percent less distance than that at which a black aircraft was seen. Williams then calculated that a white aircraft would sight a surfaced U-boat on 30 percent more occasions than a black one, which should lead to an increase in sinkings. Within a few months all Coastal aircraft used on anti-U-boat patrols were repainted with matte white leading edges and under-surfaces.

A less simple problem, and one that became a classic in the early history of operations research, was that of depth charge (D/C) settings. The prevailing assumption at Coastal Command and the Admiralty was that on average, U-boats that sighted approaching aircraft could dive to a depth of about 100 feet before an attack could be delivered. Accordingly, depth charges were set to explode at that depth. The reasoning seemed flawless until Williams discovered (1) that if a boat had gotten that deep, it would also have traveled a certain distance horizontally, with the result that a bomber would not know where to drop his D/Cs; and (2) that in about 40 percent of attacks to date the boat was on the surface or had been submerged for no longer than 15 seconds, in which case 100-foot fuse settings rendered the D/Cs useless.

After some difficulty on Williams’s part in persuading Coastal officers that if the depth-setting adjuster was turned down to the 25-foot mark, the average number of U-boats sunk per given number of attacks would increase by two and a half times, the shallower setting was gradually introduced, starting with 50 feet in July 1941, progressing to 33 feet in January 1942, and reaching 25 feet in July of that year. The changes in setting were accompanied by a corresponding increase in lethality. Commented Blackett: “There can be few cases where such a great operational gain had been obtained by such a small and simple change of tactics.”

Under Blackett the Operational Research Section (O.R.S.) at Coastal grew into a tightly knit and formidable band of scholars, which included two future Nobel Prize winners (Blackett and John C. Kendrew), five future Fellows of the Royal Society (Blackett, Kendrew, Williams, C. H. Waddington, G. W. Robertson), and one future Fellow of the National Academy of Sciences of Australia (J. M. Rendel). With the exception of Blackett, who was forty-five in 1942, all were in their twenties and thirties. These and other O.R.S. members took on a wide range of problems affecting Coastal’s performance. Nine times out of ten the O.R.S. analysis found that existing operational assumptions and procedures were soundly based. Joubert’s staff had concluded, for example, that it was a better tactic to force a U-boat pack’s convoy shadower under the surface and thus disrupt the pack’s operation while it was being organized than to wait until after an attack was made to intervene.

O.R.S. analysis was able to confirm and refine this tactic by showing that in order to do this, patrols must not be laid on too close to the convoy’s position. Studies had found, ironically, that most U-boat sightings had been made by aircraft that failed to meet their convoys. This led to the conclusion that most of a U-boat pack assembled more than twenty miles distant from the threatened convoy, and air patrols were vectored accordingly. During the period August 1942-May 1943, patrol at a distance yielded 40 percent more air attacks than continuous close escort (which was the American doctrine), greatly reduced sinkings by day, halved losses on the first night of a convoy battle and halved them again on the second, and detected a high density of boats behind the convoy, indicating that the work of the shadower had been frustrated and that the cohesion of the pack had been unhinged.

Blackett undertook additional studies of depth charge attacks (later continued by Dr. E. C. Baughan), which, like the 25-foot D/C setting, led to considerable improvement in lethality. Although Coastal personnel engaged in much discussion about bomb weight, some proposing D/Cs of 35, 100, or 600 pounds, Blackett was convinced that the current 250-pound weapon, with its 19–20 foot killing range, was perfectly serviceable if it was used correctly. He investigated its use under two categories: (1) aiming accuracy and (2) stick spacing. (A stick was a group of four to eight individual D/Cs dropped either all together as a salvo or, more often, in a series. In a series drop, an electromechanical intervalometer was used to establish the distance between the D/Cs, that is, “stick spacing.” The overall length of the D/C string was the “stick length.”)

For accuracy studies Blackett had a rear-facing mirror camera fitted to bombers and examined what the attack photographs showed, which was that pilots were placing the center of the stick length at a point 60 yards ahead of a surfaced U-boat’s conning tower. When asked why, pilots told him that it was “aim-off” to allow for the forward travel of the boat during the interval when the D/Cs were falling. This was in the manual; it was how they had been trained. But the photographs showed that the aim-off was not working. Blackett advised Joubert to have the pilots aim bang-on at the conning tower, even though it seemed to violate common sense. When they started doing so, kills increased by 50 percent.

The optimum stick spacing was a more complex problem, the resolution of which was not reached until after Blackett’s departure from Coastal Command in January 1942. Current practice of pilots was to set for 36 feet between charges, but mathematical analysis suggested that this was too short. The O.R.S. recommendation that the spacing be increased to 100 feet was accepted by the Coastal staff in March 1943, after which straddles of a U-boat with 100-foot spacing were increasingly lethal.

O.R.S. attacked many other problems, some as mundane as what came to be called Planned Flying and Maintenance, pursued by Dr. C. E. Gordon, whose aim was to make maximum possible use of crewmen and aircraft. Gordon found that in a typical squadron of nineteen aircraft only 6 percent of the time (in hours) was spent in the air; 23 percent on the ground even though crews were available and aircraft were operational; 30 percent in repair or maintenance; and 41 percent waiting on spare parts or manpower. If efficient use could be made of Coastal’s already existing resources, the force at sea could be greatly enlarged. Gordon’s “efficiency study,” as one would call it today, led to a near doubling of flying hours—a squadron of nineteen increasing from 1,300 to 4,000 hours—and proportionately greater peril to U-boats. The O.R.S. system was eventually adopted throughout the RAF and the Naval Air Division.

Other O.R.S. members, particularly the mathematicians, worked on more arcane problems, such as aircraft operational sweep rate and width; sighting ranges of various aircraft and of the various sighting positions within an aircraft; optimum altitudes for visual and radar searches; eye rest requirements for crew; probability-of-kill-given-sighting; open water navigation technique; the average number of convoys sighted by a U-boat during its lifetime (seven and a half), the average life expectancy of a U-boat (14 patrols), and development of what today would be called a “macro-model” of U-boat circulation in the North Atlantic. In January 1942, as earlier noted, Blackett left Coastal Command. His place as Officer in Charge was taken by Professor Williams. The section’s work continued as before, with what might be called even closer association of uniformed Command and civilian scientist after 6 February 1943, when Air Marshal Sir John Slessor succeeded Joubert as AOC-in-C of RAF Coastal Command.

Waddington testified that “At least in the sphere of my experience, I have rarely met such critical generosity of mind as was shown to us civilian ‘intruders.’” At no time, it appears, was there the slightest concern on the part of Joubert or Slessor that the “suck it and see” scientists sought an unwarranted prominence for themselves or ever considered themselves as anything other than members of a team.

In citing the contributions to Coastal of non-RAF personnel, special mention should be made of the senior Naval Liaison Officer, Commander, later Captain, D. V. Peyton Ward, R.N., who was the very embodiment of the close and fruitful relationship that existed between Coastal Command and the Admiralty. An invalided-out submariner, “P.W.,” as he was affectionately known at Northwood, volunteered for tasks not normally required of his position, and after Joubert’s arrival he took it upon himself to interview all returning aircrews who had sighted and/or sunk a U-boat. By writing up and analyzing each such incident, he greatly enlarged the attack data available to O.R.S. A navy-blue in the midst of RAF slate-blue, he represented Coastal Command on the important interservice U-Boat Assessment Committee, which judged the success of surface and air attacks. After the war, he wrote the official four-volume history of air operations in the maritime war. All the while O.R.S. and P.W. were bending their minds, the aircrews practiced their own difficult art of air search, hundreds of miles out over the Atlantic’s gray flannel, noisily patrolling 1,000 to 5,000 feet off the deck, in every kind of weather, dirty and cold, rarely if ever in their entire flight careers sighting a single U-boat to reward them for their protracted and boring hours. Said one crewman:

“It is difficult to describe the intense boredom of the sorties we undertook: hour after hour after hour with nothing to look at but sea. I am sure that when they found U-boats many crews pressed home their attacks regardless of what was being thrown at them, merely because it was a welcome relief from the boredom.”

And many crews would be shot down, in distant positions where no assistance was near or possible. And many other crews were lost to the sea not through enemy action, but through engine failure, adverse weather, navigational error, and fuel depletion.

Coastal Command’s motto was: “Constant Endeavor.”


The Bay of Biscay is a roughly triangular body of water bordering the Atlantic that is formed on the north by the Brittany peninsula of France, where it does an arabesque toward Land’s End on England’s Cornwall coast, and on the south by the northern provinces of Spain. About 86,000 square miles (223,000 square kilometers) in size, and 15,525 feet (4,735 meters) deep at its center, it was the body of water traversed by U-boats operating out of bases at the western French ports of Brest, Lorient, St.-Nazaire, La Pallice, and Bordeaux. Normally, outbound and inbound boats transited through a zone, or “choke point,” about 300 miles north to south and 200 miles east to west. Here, more than at any other sea position, U-boats could be found in high concentration: traffic ranged from forty-five boats per month in June 1942 to a figure that, in early 1943, passed 100 (expected to increase to 150 by spring). The Strait of Gibraltar was another choke point, but far fewer boats attempted its passage; and the northern route from Germany around the north of Scotland was another transit area, but one that was used almost exclusively by new boats coming into Atlantic service. If one wanted to find a large number of U-boats bunched up in any one place, it would be in the transit zone of the Bay of Biscay.33 In March 1943, the Admiralty said of the enemy:

“Apart from modifying his tactics, or disengaging from an attack, he can withdraw altogether from any given convoy area as he had done to a large extent in the areas off the American coast. He cannot withdraw from the Bay.”

Whether U-boats were bound to and from the midocean transatlantic convoy lanes, where the most intensive pack battles were fought, or to and from what the British called the Outer Seas—Freetown, Cape Town, the Indian Ocean, the Atlantic Narrows, Brazil, the Caribbean, and the North American seaboard—the swept channels of the Biscay minefields were the narrow funnel through which every boat had to pass. To an adversary with marksman instincts, the Bay presented an irresistible bull’s-eye.

From the date he assumed command at Northwood in 1941, Air Chief Marshal Joubert cast a malevolent glare in that direction. Like many at Coastal before him, he could not understand why Bomber Command with its heavy bombardment squadrons had not destroyed the steel and concrete U-boat bunkers while they were still under construction and vulnerable. As a matter of fact, Bomber Command did attempt to disrupt construction, making twenty nighttime raids on the Lorient base in 1940, sixteen in 1941, and twelve in early 1942. The U.S. Eighth Air Force made ten daylight raids on St.-Nazaire between November 1942 and June 1943. Other raids were mounted against Brest. All such raids were ineffectual, owing to poor bombing accuracy and to intense anti-aircraft fire that caused heavy bomber losses. The only result on the ground was the flattening of the towns where the bases were situated. Of Lorient and St.-Nazaire, Admiral Donitz said that not a cat or a dog survived. Left with the problem of nearly completed bomb shelters, Joubert decided that since Coastal Command was envisioned to be an offensive instrument and the hunter role suited his nature, he would direct as much of its power as he could spare from convoy escort to that of offensive patrol against U-boats transiting the Bay. In making that decision, he entered a debate that would never be completely resolved, either in Coastal or the Admiralty: whether ‘tis nobler to defend convoys and so win the Atlantic by seeing merchantmen to safe and timely arrivals at their destinations, or to take up arms against a sea of U-boats, and by hunting, kill them?

What came to be called the First Bay Offensive, launched by Joubert in the summer of 1941, was a daytime operation flown by RAF Coastal Command Sunderlands, Wellingtons, Whitleys, Hudsons, and Catalinas, all of them equipped with 1.5-meter wavelength ASV Mark II radar. It yielded very disappointing results. O.R.S. analysts discovered that 60 percent of the U-boats sighted the approaching aircraft before being spotted themselves, and thus were able to dive out of harm’s way. As the campaign wore on into autumn, it became clear that transiting U-boat commanders, alerted to the increased presence of aircraft in the Bay, were charging their batteries on the surface at night and traveling as much as possible submerged during the day. Sightings of boats decreased accordingly, and the record shows that the year ended without a single U-boat kill by aircraft in the Bay.

What was needed, argued Professor Blackett of O.R.S., who chaired a specially organized Night Attack Sub-Committee under the ASW Committee on Aircraft Attacks in the Admiralty, was an effective means of delivering attacks during darkness when the U-boats were on the surface charging. And that meant an illuminant that could display to the pilot’s eye targets detected first by radar. In early 1942 combat experiments were run using 4-inch flares towed by radar-equipped Whitleys, but these proved unsuccessful. Another, more promising illuminant was waiting in the wings.

When in September 1940 the then AOC-in-C Air Chief Marshal Bowhill sent around a memorandum asking officers and airmen to submit ideas for improvement of ASW operations, he received back a detailed proposal for an airborne searchlight for use in night attacks on surfaced U-boats. It came from a nontechnical source, a World War I pilot who had flown ASW patrols over the Mediterranean in that conflict, named Squadron Leader Humphrey de Verde “Sammy” Leigh, now serving as Assistant Personnel Officer in headquarters administration. Leigh proposed that the so-called DWI Wellingtons, which had earlier, but no longer, been used to explode magnetic mines from the air by generating a powerful electrical charge, be refitted with a belly-installed retractable carbon arc lamp. The DWIs recommended themselves for this use because they were already equipped with auxiliary engines and either 35-or 90-kilowatt generators.

Bowhill was so impressed by the idea that he relieved Leigh of his desk duties and set him to work full-time on the project. There were numerous obstacles to overcome, starting with the technicians at RAE, Farnborough, who argued the case for towed flares as preferable to the searchlight scheme. The nontechnician Leigh pressed on regardless, and ingeniously solved every problem that he encountered, among them ventilation of the carbon arc fumes, steering control of the lamp’s beam in azimuth and elevation, prevention of back glare, or “dazzle,” and reduction of weight. In March 1941 the Vickers plant at Brook-lands completed a prototype installation employing a naval 24-inch (61 cm) narrow-beam searchlight, giving a maximum 50 million candles without a spreading lens, powered by seven 12-volt 40-ampere-hour type D accumulators (storage batteries); and on the night of 4 May, with Leigh himself operating the light controls in the nose, the first Leigh Light Wellington repeatedly detected, illuminated, and “attacked” the British submarine H—31 off Northern Ireland. Bowhill was no less gratified at this success than Leigh, but only one month later, when Bowhill was relieved by Joubert, the whole project was canceled and Leigh found himself reassigned to a desk.

It happened that Joubert had been associated with the development of a competing airborne light system called the Helmore Light, after an RAF Group Captain, which had been designed for illuminating enemy bombers at night, and the new AOC-in-C thought it should be used against U-boats as well. But the Helmore Light was quickly shown to be unsuitable for Coastal work: its massive array of accumulators occupied the entire bomb bay; the light could not be steered, or aimed, except by moving the entire aircraft; and the brightness of the light, which was mounted in the nose, dazzled both the operator and the pilot. “After some two months I found, as I do not mind admitting,” Joubert wrote later, “that I had made a mistake.” Leigh cleaned out his desk a second time and returned to the hangar.

Months of redesign, flight testing, crew training, and what Peyton Ward called “difficult to explain” administrative delays followed, until finally, at the beginning of June 1942, a “penny packet” of five Leigh Light (L/L) Wellingtons of No. 172 Squadron entered operational service in the Bay. The first L/L-assisted attack was made on 4 June against the Italian submarine Luigi Torelli (Tenente di Vascello [Lt.-Cmdr.] Augusto Migliorini), resulting in severe damage. The attack was made by Squadron Leader Jeaff Greswell, flying Wellington “F” of 172 Squadron. During June and July the Wellington bombers, showing what the surprised and helpless Germans came to call das verdammte Licht— “that damn light”—made altogether eleven sightings and six attacks, resulting in one kill—the Type IXC U-502 (Kptlt. Jürgen von Rosenstiel) en route home from the Caribbean, sunk by Wellington VIII “H” flown by Pilot Officer Wiley Howell, an American serving with the RAF—and two boats damaged.

leigh light on a plane

Leigh Light mounted on a Sunderland flying boat

Before the Wellingtons could improve on that record, Admiral Donitz ordered his U-boats in the Bay: “Because the danger of attacks without warning from radar-equipped aircraft is [now] greater by night than by day, in future U-boats are to surface by day…. ” In a month and a half’s time the Leigh Light had taken the night away from U-boats in the Bay, but that, it turned out, would be for now their major contribution. The air war in the Bay returned to daylight hours, and with slightly better returns than before, as between mid-July and the end of September, conventionally equipped aircraft made over seventy sightings and sank three additional U-boats.

Still, the great opportunity that the Bay presented eluded Coastal’ Commands grasp. The ratio of kills to daytime sightings remained disappointingly low throughout the remainder of 1942 and well into the new year. Whereas Coastal Command had expected that with increased time given to practice attacks, with, at last, 25-foot depth pistols, and with Torpex fillings, the percentage of lethal attacks would rise to 20 percent, it hovered instead at 6 percent. The lethality problem prevailed everywhere in waters that the U-boats infested, even where attacks were made from unseen cloud approaches on Class A targets, that is, those in which the U-boat was on the surface or had been submerged fewer than 15 seconds. Coastal was divided on the question of where blame should be placed: on poor weapons or on poor aim? Rear gunner reports and photographs suggested that the 250-pound Torpex D/C did not seem to injure boats even when perfect straddles were achieved. The O.R.S., however, defended the weapon, and, after intense study, determined that, photographs seemingly to the contrary, the problem was aiming, which could be corrected by more and better training.

In support of this conclusion the O.R.S. produced evidence that three outstanding squadrons, No. 120 (6 kills, 10 damaged), No. 202 (4 kills, 5 damaged), and No. 500 (4 kills, 9 damaged) also had solid records in practice bombing. It pointed as well to certain individual pilots, such as Squadron Leader Terence M. Bulloch, of No. 120 Squadron, with three U-boats sunk and three damaged, and Flying Officer M. A. “Mike” Ensor of No. 500, with one U-boat sunk and three damaged. In each case, the former in a Liberator, the latter in a Hudson, painstaking practice had translated into successful performance in combat. There was nothing wrong with the weapon. O.R.S.'s findings set in train intensive drills in marksmanship.

Another problem that the daylight bombers had to face was an increase in opposition from the Luftwaffe, which in the summer and fall of 1942 attempted to interdict Coastal Command patrols in the Bay, employing Focke-Wulf 190s, Heinkel 115s, Junkers 88s, Messerschmitt 210s, and Arado 196 fighter patrols to cover U-Boat routes on the Bay. Some aircraft and crew casualties resulted, but No. 235 Beaufighter Squadron at Chivenor in Devon successfully fought the attackers off, and the enemy air effort died away.

The nighttime bombers, which continued busy in the Bay Offensive, had problems of their own. The first was the French tunny (tuna) fleet, which followed the shoals of tunny into the middle Bay where most of the Leigh Light aircraft were operating. Numerous A.S.V. blips, when illuminated, turned out to be tunny craft. Their radar signature was indistinguishable from that of a U-boat. Use of the searchlight in these cases not only caused a 25 percent waste of effort and ran down the electrical power in the batteries, it gave fair warning to U-boats nearby that an L/L Wellington was in the area. In August the problem was so severe that L/L missions were considered futile and Coastal attempted to warn off the fishing craft by BBC broadcasts, leaflets, and threats to shoot, but nothing worked and the interference remained intractable until the end of the tunny season in October.

In the meantime the L/L flights, indeed all flights, were confronted by a far more serious problem. Admiral Dönitz’s technical staff had concluded, correctly, that the illuminated attacks in the Bay had been made possible by airborne metric radar. Helped by an A.S.V. Mark II set captured in Tunisia, BdU technicians developed a radar receiver (Type R.600) that could detect the presence of 1.5-meter pulses and give a U-boat time to dive out of danger. In fact, it produced a warning signal at a greater range than that at which an aircraft could acquire the blip (plus or minus 10 miles). Manufactured by the Paris firm Metox (also later by Grandin), the equipment was put to sea in August on three boats, U—214, U—107, and U—69. Except for problems encountered with the antenna, which was affixed to a crude wooden crosspiece (Biskayakreuz, the “Biscay cross,” as it came to be called) that had to be carried up and down the tower ladder when surfacing and diving, causing troublesome delays, the three boats reported favorably on the device’s effectiveness. Donitz then ordered the equipment fitted to every boat in the fleet, a process that was nearly complete by the end of the year. This logical German countermeasure enabled the boats to resume surfacing by night.

A dramatic falloff in Coastal Command sightings, both day and night, together with intelligence drawn by Winn and Beesly from naval Enigma, gave Northwood a strong clue to what had happened. The value of the Bay campaign in these circumstances came under strong questioning, and AOC-in-C Joubert pressed London hard for 10-centimeter equipment with which to defeat the German Search Receiver (G.S.R.). But the first squadron to be so equipped did not become operational until the following March 1943. In the meantime, Coastal relied on the only expedient available: flooding. In this tactic all the aircraft over the Bay except the L/L Wellingtons, which, it was hoped, might catch a U-boat off its guard, were to use their A.S.V. continuously. The expectation was that with the G.S.R. alarm ringing without stop, U-boats would not know when they were being targeted—an alarm that rang all the time was as useless as one that rang not at all—and so might become complacent or careless. But the tactic did not lead to additional sightings and attacks. In fact, during January 1943 a total of 3,136 day hours led to only five sightings, and 827 hours of combined L/L and conventional night patrols produced only three sightings. These were a new low record in the Bay.


During the U-boats’ six-month-long picnic on the North American seaboard, overstretched and weary RN surface escorts had a respite in which to fit new detection gear, practice use of weapons, including, on some ships, the new Hedgehog, and train ranks and ratings. The ratings’ first training experience, and in many cases, their first glimpse of the sea came when newly commissioned escort vessels received their working up at HMS Western Isles in Tobermory harbor on the Isle of Mull off the west coast of Scotland. There the legendary (and quirky) Commodore Gilbert “Puggy” (or “Monkey”) Stephenson took callow “Hostilities Only” landlubbers—1,132 groups in all during the war— and, within two to three weeks’ time, shaped them into disciplined, semiskilled seamen who went directly into convoy escort service.

‘While Stephenson’s work with new crews did not require a respite from combat to carry on, the efficiency training of Captains and Watch-Keeping Officers did. This was particularly true of the Western Approaches Tactical Unit (WATU), an operational ASW analysis facility established at the suggestion of Churchill in January 1942, coincidentally the beginning month of the U-boats’ American campaign. The facility was erected on the bomb-damaged top floor of the Tate and Lyle Exchange Buildings to the east of Commander-in-Chief Western Approaches (CinCWA) in Derby House, Liverpool. To organize and direct the WATU, Churchill sent an RN Commander (later Captain) named Gilbert Howlands Roberts who, like Peyton Ward at Northwood, had been invalided out of the Navy, in his case because of tuberculosis.

A former destroyer Captain who was trained as a gunnery officer, Roberts modeled his facility on the floor plot used at gunnery school. He divided off a large linoleum-covered floor representing the open sea with lines ten inches apart indicating miles, and placed on that “Tactical Table” wooden models of convoy ships, escort vessels, and U-boats. Then, with canvas and string, he screened off any view of the ocean except for small apertures that gave only restricted views of an operational situation, akin to the restrictions prevailing at sea, particularly at night. Twenty-four “players” could work at the full floor plot, or three groups of eight players each could work at partitions of the plot. They sat at plotting tables around the viewscreens.

While a staff mainly of seventeen-to twenty-year-old Wrens (Women’s Royal Naval Service, or WRNS) manipulated both the models and the views allowed of them, combat situations were simulated and escort group Captains and Watch-Keeping Officers were asked to make decisions about appropriate actions to take in the circumstances shown—the circumstances being based on intensive interviews Roberts had conducted with Senior Officers of Escort Groups. Every movement was tracked, those of the U-boats in green chalk, those of the escorts in white, so that at the conclusion of “The Game,” as the exercise was called, the participants could inspect their successes and failures in pursuit and attack. The tactical course lasted six days, and as the months progressed, the teenage Wrens gained sufficient competence to be able, discreetly, to advise sea-hardened officers on what might be their next best course of action—as remembered by a Lieutenant (later novelist) named Nicholas Monsarrat, who allowed in his The Cruel Sea, “Rather unfairly they seemed to know all about everything…. ”

Numerous innovative attack procedures evolved from these exercises, the first of them based on reports of U-boat attack behavior during the passage of Convoy HG.76 from Gibraltar to the U.K. in December 1941 that were given Roberts by an offensive-minded Senior Officer Escort (SO) named Commander (later Captain) Frederic John Walker, who commanded the convoy’s Escort Group 36. Whereas Walker’s escorts thought that a U-boat that attacked HG.76 was about a mile outside the convoy, Roberts deduced from a simulation on his plot that the boat attacked from within the convoy columns, having infiltrated from astern. He thereupon devised a countermeasure to catch such a boat as it attempted escape. Since one of the Wrens suggested that the new tactic would give a “raspberry” to Hitler, Roberts assigned it that name. CinCWA Admiral Noble informed Churchill of this correction to “a cardinal error in anti-U-boat tactics” and within twenty-four hours signaled instructions for Raspberry to the Fleet.43 This tactic and a modification called Half-Raspberry were the first universally prescribed escort counterattack maneuvers; prior to their decree each SO was free to devise his own maneuvers. Soon, after trials on the Tactical Table, other fruit-named tactics were developed: “Pineapple,” “Gooseberry,” and “Strawberry”; to be joined by “Beta Search,” “Artichoke,” and “Observant.” Meanwhile, sea training in these maneuvers went on at Londonderry, Greenock, Birkenhead, Freetown, Bombay, St. John’s, Newfoundland, and Sydney, Nova Scotia, where escort groups practiced as teams under their own SOs.

It was these finely honed escort teams who met the U-boat men when the latter returned in force to the mid-Atlantic in early August, 1942. The slugging match between these two old enemies from that date until the start of May 1943 was fierce and relentless, but, as already indicated in this chapter and in the prologue, neither side was able to deliver a knockout blow. Nor was the renewed German effort against convoys limited to the major transatlantic trade routes. Admiral Donitz probed for soft spots in the Outer Seas where Allied defenses might have been attenuated by the need to reinforce the northern lanes; thus, he deployed boats to Freetown, Cape Town, and Madagascar, to the Atlantic Narrows between West Africa and Brazil, to the Brazilian and Panamanian coasts, and to the traffic area eastward of Trinidad in the Caribbean.

In raw numbers the U-boats enjoyed commendable successes. During August, with 86 boats at sea, the U-Bootwaffe made an impressive number of convoy contacts per boat and sank 105 ships for 517,295 GRT; and in November, as noted earlier, the boats scored their highest monthly total of tonnage sunk in the entire Atlantic war. But throughout the period August 1942 to April 1943, their ever-increasing number of operational boats at sea generated diminishing returns in tonnage sunk per boat per day at sea—this despite the fact that U-tankers in midocean were multiplying their days at sea, deferring their maintenance, alleviating operational delays caused by the backlog of boats needing fuel at base, and frustrating Coastal Command’s Bay Offensive by eliminating the need for two transits per boat through the Bay. (In the twelvemonth period prior to the end of May 1943 the supply U-boats replenished 220 U-boats operating against Atlantic convoys as well as 170 boats assigned to Outer Seas.

All the while, the experience and proficiency levels of the U-boat crews were declining, owing both to losses and to rapid expansion, while those of the escort crews were waxing, thanks in great part to the intense training regimen of January-July 1942, and to the fitting during the same period of new equipment such as HF/DF and 10-centimeter radar. From August through April 1943 the U-boats were being sunk at a monthly rate of 9.7, including February’s record 19. In the same period, three out of four ocean convoys made port without loss and 90 percent of those convoys that were attacked similarly reached their destinations. German intelligence and BdU completely missed the military convoys of the Anglo-American expeditionary force (Operation Torch) that sailed from the U.K. and the U.S. beginning on 18 October and effected landings on 8 November in French Northwest Africa, at Casablanca in Morocco, and at Oran and Algiers in Algeria. Only one of the 334 ships that participated was attacked by a U-boat, and it by accidental encounter. German records do not disclose a single sighting, even inkling, of that armada as such.

CU New York-CuraCao-United Kingdom.
GU Alexandria-North Africa-U.S.A.
HG Gibraltar-United Kingdom.
HX Halifax-United Kingdom.
KMF United Kingdom-North Africa-Port Said (Fast).
KMS United Kingdom-North Africa-Port Said (Slow).
KX United Kingdom-Gibraltar (Special).
MKF Mediterranean-North Africa-United Kingdom (Fast).
MKS Mediterranean-North Africa-United Kingdom (Slow).
OG United Kingdom-Gibraltar.
ON United Kingdom-North America.
ONS United Kingdom-North America.
OS United Kingdom-West Africa.
SC Halifax-United Kingdom (Slow).
SL Sierra Leone-United Kingdom.
UC United Kingdom-Curaçao-New York.
UG U.S. A.-North Africa.
UGF U.S.A.-North Africa.
UGS U.S.A.-North Africa.
UT U.S.A.-United Kingdom (Military).
WS United Kingdom-Middle East and India (Military).
XK Gibraltar-United Kingdom (Special).
EC Southend to Clyde, Oban or Loch Ewe (Coastal Convoys, North about).
WN Clyde, Oban or Loch Ewe to Methil (Coastal Convoys, North about).

Donitz, who had expected a possible Allied action at Dakar, and had stationed boats in the Freetown and Cape Verde Island zones as a precaution, found himself on 8 November completely out of position. His rushed disposition of boats to the Moroccan Atlantic coast and to the western approaches of Gibraltar to attack new supply shipping and thus strangle the invasion buildup led to the sinking of ten merchant ships, four transports, and five warships—including Werner Henke’s fleet repair ship HMS Hecla on n/12 November—but at terrible cost: eight U-boats sunk, 19 damaged, and one Italian submarine sunk. With such thin results attended by disproportionately high losses, Donitz pulled his boats in early December for assignment to more productive areas of the Atlantic.

Three notable command changes took place in the fall and winter of 1942–1943. On 17 November 1942, Admiral Sir Max Horton, since December 1939 Vice-Admiral (later Admiral) Submarines, succeeded Percy Noble as CinCWA (Commander in Chief Westertn Approaches Command Royal Navy). Noble was named Chief of the British Admiralty delegation (BAD) in Washington. Horton had earlier turned down C-in-C Home Fleet because he thought that post to be too much under the thumb of Whitehall. At Submarine Command in Northways, Hampstead, he had forged close working ties with Coastal Command at nearby Northwood, and during three years of war became convinced “that fleets cannot operate without the close cooperation of air power”—a conviction that he would translate into deeds at Western Approaches.

Upon his arrival at the large gray block of buildings that was Derby House, he inspected its facilities, including the armored and gasproof Operations Room in its basement, and called for the principal officers to explain their duties. To Gilbert Roberts of the Tactical School he said, “What do you think you do?” Roberts replied, “Why don’t you come up and see properly?” Horton did, and at 9:00 the next morning he returned unattended to begin the six-day course. Not everyone so impressed Horton, however, and more than a few officers fell victim to deadwood cutting.

Admiral Max Horton

Admiral Max Horton , Commander in Chief of Wesrtern Approaches Command after 17 November 1942 and winner of Battle of Atlantic (it is amusing that everyone knows the losing side’s leader Donitz since he published his Memoirs after the war when he was reeleased from prison in 1956 but Horton who won the Battle of Atlantic remained unknown since he did not publish his memoirs before his untimely death in 1951)

Horton’s mandate as CinCWA was: “the protection of trade, the routing and control of all convoys and measures to combat any attack on convoy by U-boats or hostile aircraft within his Command.” (Military convoys and fast troopships remained under the control of the Admiralty.) He also saw as his responsibility the improvement and intensification of training. Early in February 1943 he received a yacht, HMS Philante, and a submarine, sometimes two, with which, in effect, to take Roberts’s Tactical School to sea. At Larne in Northern Ireland each Escort Group prior to joining its convoy was put through exercises designed by Captain A. J. Baker-Creswell, R.N., to represent actual combat conditions to be encountered. What was more, the exercises were conducted in close cooperation with Coastal Command aircraft, in order to perfect navigation and rendezvous, TBS and signal code communications, and joint attack procedures. Furthermore, surface-air collaboration was to be practiced even while with the convoys en route. And the surface Escort Groups, a Percy Noble innovation, were to be kept together as teams.

Another Noble innovation that, except for one prototype, had not been possible to implement in his predecessor’s time for lack of assets was Support Groups—small, highly trained, and offensively minded flotillas of destroyers, sloops, frigates, and cutters that would ride to the rescue of convoys and Escort Groups directly menaced or under attack. In Noble’s vision such groups would include, when they became available, auxiliary aircraft carriers. Horton embraced the concept and wrote almost daily to the Admiralty begging for ships to make the forces possible, eventually succeeding in obtaining the loan of a number of Home Fleet destroyers. To these he took the risk of adding sixteen warships obtained by reducing the strength of each Escort Group by one vessel. The result was, at the end of March, five Support Groups fully trained and ready to fulfill their sole mission: hunt down and kill U-boats.

Meanwhile, in his glass-fronted office facing the Operations Room, Horton had constant access in an adjoining office to Air Vice Marshal Sir Leonard H. Slatter, commanding No. 15 Group, whose squadrons covered the North Atlantic convoy lanes from bases on the West Coast of Scotland, in the Hebrides, and in Northern Ireland, with a detachment at Reykjavik. Both men lived on the premises, though Slatter did not follow Horton’s somewhat eccentric daily schedule, which had him on the golf course all afternoon, at the bridge table after dinner, and in his office by 2330, usually in “worn and split” pajamas, drinking barley water while directing convoy battles on the huge wall plot opposite, and with, as one observer said, an “uncanny prevision” of what the U-boats would do next. Different in manner from the urbane and kindly Noble, for whom everyone at Derby House had affection as well as respect, especially the Wrens, Horton’s behavior prompted such descriptions as “ruthless,” “determined,” “selfish,” “intolerant,” “perfectionist,” and “maddening.” Apparently the flinty old submariner was just the type Churchill thought should lead the surface and air escorts into the dangerous new year—“a thief to catch a thief,” as it were.

The second major command change affected that other thief, Karl Dönitz at BdU. When in December Adolf Hitler harangued Grossadmiral Erich Raeder, Commander-in-Chief Navy (Oberbefehlshaber der Kriegsmarine), over the failure of a surface force led by two heavy cruisers to advance successfully against an RN Arctic convoy escort screen, and went on to threaten the scrapping of all big ships in the fleet, the proud Hamburger veteran of the Imperial Navy and Battle of Jutland tendered his resignation, which the Führer, though surprised, accepted. On 30 January 1943 Dönitz was named Grossadmiral and C-in-C in his stead, while retaining his command as Flag Officer U-Boats. Now Dönitz had direct access to Hitler, whom he could importune for steel and shipyard workers; he had authority over the Naval Staff, Seekriegsleitung (Skl), whose approvals he need no longer seek; and he had freedom to prosecute the Tonnageschlacht without diversion of his forces to unprofitable waters. Just the preceding month he had written in his war diary: “The tonnage battle is the main task of the U-boats…. It must be carried on where the greatest successes can be achieved with the smallest losses.”

But the new appointment also had its disadvantages, principally, as Raeder, who nominated him for the post predicted, that as C-in-C Dönitz “would not be able to dedicate himself to the immediate conduct of the U-boat war to the same extent as formerly.” The “Lion,” as U-boat men admiringly called him, had already suffered physical distancing from his underseas fleet and their crews, when in March 1942 a British raiding party attacked St.-Nazaire; alerted to how easily such a raid might be made on BdU itself, Dönitz reluctantly abandoned Kernével and established his headquarters in an apartment complex on the Avenue du Maréchal Maunoury in Paris. Now, to consolidate BdU with his new post as C-in-C, he moved U-boat headquarters even farther east, to the Hotel am Steinplatz in the Charlottenburg suburb of Berlin (losing two railroad cars filled with equipment and papers in the process), where BdU became operational on 31 March 1943. It had been Dönitz’s presence on the dock at Lorient and the other bases, where he attended to his crews’ leavings and returnings, that cemented his standing as a father figure to his men and elicited a depth of loyalty from ranks and ratings that was unprecedented in the Kriegsmarine. Now his inspiring figure and voice were far from the bases, with what negative impact it is impossible to calculate.

With his longtime Chief of Operations Branch (BdU-Ops), Konteradmiral Eberhard Godt, Dönitz incorporated BdU into the Naval Staff as its Second Section, with Godt, Chief of Staff, overseeing day-to-day conduct of U-boat operations—although in the war diary, where major convoy battles are described and where strategies or policies are declared, one continues to hear the voice of Dönitz, with the result that in the chapters that follow in this narrative the citations of passages from the diary assume their authorship by a Dönitz/Godt duumvirate. The entire BdU operations staff numbered barely more than a dozen officers, most of them in their early thirties (Dönitz was 51, Godt 42). Though it could draw upon the much larger Naval Staff for such things as Intelligence (3/Skl), Communications Service (4/Skl), Radar Countermeasures (5/Skl), and Meteorology (6/Skl), it remained a thin blue line for trying conclusions with the combined staffs of the Admiralty and Coastal Command, not to mention GC&CS. (Western Approaches alone had a staff of over a thousand officers and ratings.)

The third major change in command came in RAF Coastal Command, where Joubert was succeeded as AOC-in-C by Air Marshal Sir John Slessor on 5 February 1943. A Royal Flying Corps pilot in the Kaiser’s war, Slessor had fought off Zeppelins over London and flown artillery observation missions over the trenches of France. His most recent posts in the Führer’s war were Commander of 5 Group of Bomber Command and Assistant Chief of the Air Staff (Policy). With Air Chief Marshal Sir Charles F. A. Portal, Chief of the Air Staff, he attended the Casablanca Conference, actually held in a residential suburb of the city called Anfa, where, from 14 to 23 January, Churchill, Roosevelt, and their Combined Chiefs of Staff conferred on the priorities to be established for future operations. He was present when the conferees approved their final Memorandum, “Conduct of the War in 1943,” with, at its head, the now well-known “First Charge” declaration: “The Defeat of the U-boat must remain a first charge on the resources of the United Nations.”

Slessor wrote after the war that the person responsible for having that strategic imperative given first ranking was Admiral Ernest J. King, though King’s biographer does not mention it, except to say that, “Everyone agreed that the Battle of the Atlantic took first priority.” Slessor did not think that the “First Charge” declaration had much practical influence on the anti-U-boat war, except to prod the Air Ministry to divert some of the newly available centimetric radar sets from Bomber to Coastal Command. It was not until March, however, that the first Coastal squadron equipped with 10-centimeter ASV Mark III became operational. That squadron, which flew L/L Wellingtons, was then in a position to defeat the Metox receiver, and so surprise the surfaced U-boats at night as L/L aircraft had done up to six months before. The pure hunt was on again. Or was it?

The Admiralty pressed Slessor to make immediate and maximum use of the centimetric aircraft in the Bay of Biscay, and to take full advantage of the interval of time before the Germans developed a new search receiver to detect 10-centimeter pulses. But Slessor balked at going back to the Bay Offensive, as he stated in a Note to the Prime Minister’s Anti-U-Boat Warfare Committee, of which he was a member. The A.U. Committee, as it came to be called, had been formed subordinate to the War Cabinet on 13 November and thereafter met weekly at No. 10 Downing Street under the Chairmanship of the Prime Minister. Its membership was composed of (with varying attendance and occasional visitors) twenty-two Ministers, Admirals, and Air Marshals, together with the scientists Blackett, Watson Watt, and Lindemann (now Lord Cherwell), and Mr. Averell Harriman, President Roosevelt’s personal envoy to the United Kingdom.

To this top-level body, on 22 March, Slessor sent his five-page Note accompanied by a twenty-five-page statistical analysis of the Bay Offensive from June 1942 to February 1943 and of the air cover given threatened convoys from September 1942 to February 1943. The analysis had been done by Coastal’s O.R.S., then headed by Professor Waddington, which Slessor valued and supported no less than Joubert. The analysis showed, wrote Slessor, that whereas on the Bay patrols there had been one sighting of a U-boat for every 164 hours flown in the period June to September, and one sighting per 312 hours from October to February, there had been one sighting per only 29 hours flown over threatened convoys. While the Bay patrols of No. 19 Group (Air Vice Marshall Geoffrey Bromet) had resulted in a certain number of kills, the lethal rate was a low 7 percent of attacks made, hardly justifying the disproportionate and uneconomical effort employed. Slessor therefore proposed reducing the scale of the Bay Offensive. “Our policy,” he concluded, “should be to concentrate the greatest practicable proportion of our available resources on close cover of threatened convoys, the Bay patrols assuming the position of a residuary legatee.”

When on 24 March this recommendation was placed on the table by the A.U. Committee for discussion one week hence, the Admiralty found themselves rebuked in their desire to pass from the defensive to the offensive in the U-boat war by going full-bore in the Bay. This was all the more vexing since Slessor’s Command was technically under the operational control of the Admiralty. One week later, however, as shown in chapter 8, Their Lordships would be back with a counter-strike—and the Americans alongside them.


Professor Blackett left the O.R.S. of Coastal in January 1942 to become Chief Advisor on Operational Research (C.A.O.R.) to the Admiralty. In that capacity he recruited a prestigious scientific team similar to that at Coastal—Evan Williams would follow him to Whitehall in January 1943—and cast his practical intellect across the whole range of naval operations, including, in a notable study, the optimum size of convoys. For years the number of ships in convoy had hovered at around forty-five, though the origin and rationale for that rule could not be found by Blackett. A formation larger than that was assumed to be dangerous, since it presented so many targets.

When in late autumn 1942 Blackett investigated convoy statistics for the two-year period 1941–1942, he was startled to find that convoys averaging thirty-two ships had 2.5 percent losses, but that convoys averaging fifty-four ships suffered only 1.1 percent losses. Those figures offended common sense, and Blackett knew that his team would have to develop convincing reasons to explain them. One reason was readily apparent: while the fifty-four-ship convoy occupied a larger sea area than a thirty-two-ship convoy, the guarded perimeter of the area did not expand by the same proportion. And several weeks of hard analysis produced these findings:

It was found: (a) that the chance of a convoy being sighted was nearly the same for large and small convoys; (b) that the chance that a U-boat would penetrate the [escort] screen depended only on the linear density of escorts, that is, on the number of escort vessels for each mile of perimeter to be defended; and (c) that when a U-boat did penetrate the screen, the number of merchant ships sunk was the same for both large and small convoys—simply because there were always more than enough targets. These facts taken together indicated that one would expect the same absolute number of ships to be sunk whatever the size of convoy, given the same linear escort strength, and thus the percentage of ships sunk to be inversely proportional to the size of the convoys. Hence the objective should be to reduce the number of convoys sighted by reducing the number of convoys run, the size of the convoys being increased so as to sail the same total number of ships.

Even with these data in hand, Blackett had difficulty convincing the Naval Staff to enlarge the size of convoys, since the staff worried about the vulnerability of a sixty-ship convoy to frontal attacks, an increasingly popular U-boat tactic, as well as about communication and control problems. He eventually won them over, however, and the Admiralty, in turn, at the 3 March meeting of the A.U. Committee, gained that body’s approval to start running sixty-or-more-ship convoys on a case-by-case basis, as would be done. A sixty-one-ship convoy, HX.231, departed Halifax on 29 March escorted by one frigate (SO), one destroyer, and four corvettes (Escort Group B7; see chapter 4). Helped by a Support Group and Liberators bombers air cover, it arrived at Londonderry 95 percent intact. Blackett wrote later that it was unfortunate he had not appreciated the importance of the convoy size question much earlier than he did. During the preceding year alone 200 ships might have been saved.

In a report to the A.U. Committee dated 5 February, Blackett threw himself into the defense versus offense debate that was then brewing in all the pertinent Commands. Without taking sides, he presented the “defensive values” of saving ships and the “offensive values” of attacking U-boats. Briefly stated, the defensive value of the surface escorts was found, first, by noting that shipping losses in the North Atlantic during the last six months of 1942 were at a rate of 210 ships per year, while the average number of escorts was 100. Since the statistics showed that the number of ships torpedoed per submarine present in an attack decreased as the escort force increased, and that an increase of the average escort strength from six to nine would be expected to decrease the losses by about 25 percent, had there been an additional 50 escorts available in the time period cited losses should have been reduced by fifty-ships (25 percent). Or, expressed differently, each escort vessel would have saved about one ship a year.

In determining the offensive value of surface escorts, the assumption was made that the sinking of a U-boat saved the shipping it would have sunk in subsequent months. If the escorts sank seven and damaged eight U-boats, and the eight damaged could be considered the equivalent of two additional boats sunk, since the statistics showed that about 0.4 ships were sunk per month by each operational boat, an average of 3.6 ships were saved by the sinking of a U-boat. In their offensive role the 100 escorts saved about 0.7 ships per escort vessel per year. A comparison of the defensive and offensive numbers gave the edge to the defense. Where aircraft were concerned, Blackett made similar assumptions and calculations. Using air cover over threatened convoys in the period cited, for defensive value, he calculated that each long-range aircraft in its average life of forty sorties saved about thirteen ships by defensive action. By contrast, where aircraft conducted hunting operations independent of convoys, for example, the Bay Offensive and other search and attack sweeps, the offensive value obtained from the maximum number of sorties flown by one aircraft was about three ships saved. Again, the results favored the defense.

All through March and April the defense-offense question was debated at Western Approaches, where there was increasing criticism that the current policy—“The safe and timely arrival of the convoy at its destination is the primary object of the escort”—was insufficiently bold. Even the role of the Support Groups as ancillary to the close escorts was thought by some to be a waste of their aggressive potential. Admiral Horton, whom no one could accuse of lacking in offensive spirit, and who longed for the day when he could simply “attack and kill,” nonetheless approached the question carefully, mulling over what was known of recent enemy contact and behavior.

During April sixteen convoys were attacked and suffered loss, in no case severe, however; the largest number of ships torpedoed in any one convoy was four. Of those, seven were transatlantic convoys (HX.231–234 inclusive, ON.176 and 178, and ONS.3). The typical U-boat Commander still preferred to attack on the surface at night despite the fact that radar and snowflakes (illuminants) had made that a more hazardous action than it was the year before. The U-boats now strove to get ahead of a convoy, apparently so that they could attack submerged if success on the surface seemed unlikely. In making follow-up attacks, U-boats took advantage of the disturbance created by first attacks, and they displayed a tendency to follow one another in from the same direction, from a mile or two back. Boats detected and driven off by the escorts at night frequently made no additional attempts to attack during the remainder of the night; thus, the boats had only to be detected for the battle to be half-won.

With present enemy policy, most attacks developed in front of the beam of the convoy. The U-boats were attacking more eastbound than westbound convoys, no doubt because the latter carried no cargo and were under first-class air protection for the first 600 miles of their run. Their tendency was to operate primarily in the area between 500 and 700 miles to the northeast of Newfoundland, presumably to be outside the range of aircraft based in Iceland and Ireland, air cover from Newfoundland not apparently being much of a concern to them.

Horton then considered various aspects of escort work: Practically every U-boat sunk during the past year was destroyed prior to its attack on a convoy, not afterward. U-boats were most effectively dealt with when they were on the surface, now that asdic was no longer the escort’s only weapon; therefore, forcing a U-boat to dive was not always the best policy. Analysis of asdic figures on lost contact for the last six months of 1942 showed that sixty-four percent of boats were at depths of less than 200 feet when lost. And since the morale of the Merchant Navy was showing signs of strain, it was undesirable to use convoy ships as “bait,” that is, to accept the sinking of merchant ships as a way of indicating the presence of a U-boat so that it might be attacked.

With that, however, Horton in effect threw up his hands. None of the recent data were any help in resolving the defense-offense question. To defend or to hunt? He finally decided that the Tactical Policy “must still be the safe and timely arrival of the convoy.” But there was no reason he could not have it both ways. He left the Escort Groups open to “exercise their initiative under all circumstances,” thus giving them authorization to take such offensive action as seemed prudent, necessary, and opportune, while making certain that the convoys under their care were not unduly exposed to enemy attack. “The matter was largely a question of numbers,” he wrote in a signal sent on 27 April to all British and Canadian Escort and Support Groups under CinCWA. “Whatever form of warfare is considered, the question of the strength of the opposing forces must play a very large part in deciding whether an offensive or defensive role can be adopted.” The defense-offense question, then, would not be decided at Derby House. It would be decided at sea.


The Battle for ONS.5

The safe and timely arrival of the convoy at its destination is the primary object of the escort. Evasion attains the primary object, and should therefore be the first course of action considered. At the same time, it must be borne in mind that if enemy forces are reported or encountered, the escort shares with all other fighting units the duty of destroying enemy ships, provided this duty can be undertaken without undue prejudice to the safety of the convoy. ATLANTIC CONVOY INSTRUCTIONS

FORTY-THREE MERCHANT SHIPS that would make up Outward North Atlantic Slow Convoy Five, abbreviated ONS.5 and code-named MARFLEET, assembled for their voyage on 21–22 April. Destination: Halifax, Nova Scotia, with detachments to Boston and New York. Mostly gray in color, their names painted out, they had sailed from five different ports—Milford Haven, Liverpool, the Clyde, Oban, and Londonderry—and now had rendezvoused off a lighthouse-crested rock called Oversay that rises from the sea at the North Channel entrance between northeast Ireland, the southern isle of the Inner Hebrides, and the Mull of Kintyre. There, over a twenty-four-hour period, the convoy Commodore J. Kenneth Brook, R.N.R., formed his charges, three and four deep, into a broad front of twelve columns. At the center, in column six, Brook stationed himself ahead in the Norwegian ship Rena, with only the New York-bound American oiler Argon astern.

Most of the ships were elderly tramp steamers. Most were British, but McKeesport, West Madaket, and West Maximus, as well as Argon, were of United States registry; Bonde, Rena, and Fana were Norwegian; Berkel and Bengkalis were Dutch; Agios Georgios and Nicolas were Greek; Ivan Topic Yugoslav; Isabel Panamanian; and Bornholm Danish. Two ships, McKeesport and Dolius (British), had been with SC.122 when that convoy was savaged by U-boats on 17–20 March. There was not a ship at R/V Oversay that had not sailed in convoy before. The majority were steaming in ballast, bound eventually for North and South American ports where they would load up food, fuel, raw materials, and finished weapons. Seven ships carried coal (“coal out, grain home”), four had general cargoes, and one listed general cargo and clay. Three ships in addition to those at Oversay were to join the formation at sea from Reykjavik, Iceland, on 26 April: Gudvor, Bosworth, and the U.S. Navy tanker U.S.S. Sapelo, which was returning to the States in ballast. Most of the convoy vessels were Defensively Equipped Merchant Ships (D.E.M.S.) with single four-inch guns manned by Navy and Army gunners. Gross Register Tonnage varied greatly, from tiny Bonde at 1,570 tons to the largest freighters at plus or minus 10,000 GRT.

Whatever their size, the merchantmen were expected, once underway, to maintain a speed of seven and a half knots, though their Masters knew, with gale-force seas forecast along the westward course, that was not a likely prospect. The ships’ crews also varied in composition, most of them British Merchant Navy, some U.S. Navy and Merchant Marine, others East Indian or Asian in whole or in part except for officers. Most crew had small canvas “panic bags” for carrying their most valued possessions into the lifeboats, if that became necessary; the Americans’ bags were more the size of railroad luggage.

By 1200 on 22 April this unexceptional, businesslike merchant fleet was formed up at Oversay with 1,000 yards separating the columns and 800 yards between each ship ahead and astern. The entire formation occupied eight and three-quarter square nautical miles. The shepherd, Commodore Brook, had gathered his flock. Now he awaited the sheepdog, who, he hoped, would hold the sea wolves at bay. At 1400 the sheepdog arrived in the person of Commander Peter Gretton, R.N., Senior Officer Escort, aboard the destroyer HMS Duncan, accompanied by the frigate HMS Tay, the corvettes HMS Loosestrife, HMS Pink, HMS Snowflake, and HMS Sunflower; two rescue trawlers, Northern Gem and Northern Spray, and the tanker British Lady.

Together, the warships made up Escort Group B7, the midocean close escort screen charged with seeing convoy ONS.5 to a “safe and timely arrival” at its assigned destination on the opposite shore.’ A second destroyer, H.M.S. Vidette, had been sent ahead to escort the two freighters and the USN tanker from Iceland to a midocean rendezvous with the main body. HMS Vidette’s Captain, Lieutenant Raymond S. Hart, R.N., was the only regular officer besides Gretton in the group. Two corvette Captains were Australians, one was Canadian; several officers were New Zealanders.

Thirty-year-old Peter William Gretton was educated at the Dartmouth and Greenwich Royal Navy colleges, and, rather than select a career specialization, which was the usual route to promotion, he chose to remain a general seaman officer, or “salt horse.” In a nod to specialization he learned to fly and amassed fifty hours of solo time, though he pronounced himself “not a good pilot.” In 1936 he earned a Distinguished Service Cross (DSC) leading a landing party at Haifa during the Arab rebellion in Palestine. Three years later, as war with Germany loomed, he did a week’s course in anti-submarine warfare at Portland, HMS Osprey. That experience, together with his flying, would give him a leg up in understanding the U-boat war when it came. His hankering had always been for destroyers, and he counted himself lucky to be appointed First Lieutenant of the famous destroyer HMS Cossack, on which he served in the Second Battle of Narvik, where he was mentioned in dispatches. In 1941 he received his own destroyer command on HMS Sabre, and entered convoy escort duty full-time. Transferred to command of the destroyer HMS Wolverine in 1942, he helped escort the celebrated Malta convoy(Conhvoy Pedestal which I wrote in detail in anotther thread) in August of that year and, while steaming in the Mediterranean at 26 knots, rammed and sank the Italian submarine Dagabur, with the loss of all hands, for which action he was awarded the first of three Distinguished Service Orders (DSOs).

During the weeks when the crumpled bows of HMS Wolverine underwent repair, Gretton took the anti-submarine warfare course devised by Captain Roberts at the Tactical Unit in Derby House, Liverpool. The schooling was a turning point for Gretton in several ways. First, he learned how unaware he had been of German submarine tactics and of the best means for frustrating them by use of the latest shipborne detection and weapons technology. Under Roberts’s tutelage, he quickly filled in the knowledge gaps.

Above all, Roberts stressed, effective ASW seamanship meant learning how, perhaps for the first time, to think. War at sea had changed. Courage and endurance were no longer enough. Victory over the U-boat required the intelligent use of technical aids, particularly HF/DF, 10-centimeter radar, and asdic, in that sequence. Second, Gretton realized at Derby House how much convoy duty had been denigrated by the regular Navy, which esteemed big ship-big gun fleet actions and considered the passive tending of seaborne trade as beneath their dignity, with the result that all the best officers went to the Home and Mediterranean fleets, while the failed careers and incompetents ended up in Western Approaches—with certain very notable exceptions, for example, Captain Frederic John Walker, R.N., and Captain Donald Macintyre, R.N., salt horses like Gretton. There was a desperate need in the Atlantic of more good regulars, he concluded (and when, belatedly, in 1943–44, the Home Fleet regulars realized that the Atlantic was where the war was, they climbed over each other to get Escort Group commands). Third, Gretton determined that if ever he received an Escort Group command of his own, he would bring his regular and reserve officers up to Roberts’s—and now his—exacting high standards.

Commodore Peter Gretton

Commander Peter Gretton , CO of Escort Group B7 that led critical passage of Convoy ONS.5

That brass hat came in December 1942 when he was advanced to command of Escort Group B7, based at Londonderry. There he embarked in the new twin-screw River class frigate HMS Tay, while the destroyer assigned to him, the eleven year-old, 329-foot, D-class flotilla leader HMS Duncan, was refitting in Tilbury docks prior to recom-missioning. The B7 Group had just come off a rough convoy engagement in which the Senior Officer Escort (SO) and his ship had been lost, but Gretton found his ships to be “in great heart.” Throughout January, February, and March, a period of expanding U-boat activity, he led them on cross-Atlantic passages that were, ironically, eventful for their lack of U-boat contacts. “For three months the group ran hard but had nothing to show for it but rust,” he wrote later. “We seemed always to steer clear of the wolf packs, which were then at the height of their success.”

Aboard HMS Tay he had his first sea experience with an HF/DF set. The Type FH3 equipment could identify the general position of a U-boat transmitting to base or to another boat on a high-frequency wave band, even indicate whether the U-boat was near or far. More exact “fixing” of a U-boat’s position required the “cross-cut bearing” provided by a second HF/DF-equipped ship, as Duncan would be when recommissioned. Between sailings Gretton worked his officers and technical ratings hard at Londonderry’s asdic and depth charge trainers, radar and HF-DF detection simulators, and the new Night Escort Attack Teacher, where all ranks and ratings who manned detection and communications equipment, the plotting table, or the bridge received intensive and realistic attack drills in nighttime conditions. Time and again they practiced on land the tactical maneuvers they would have to carry out at sea, which bore such code names as Raspberry, Half-Raspberry, Observant, and Artichoke.

Gretton was relentless in the conduct of these exercises and he was quite prepared to sack anyone who flagged in the effort. Among his Captains he had the reputation of an egotist but a gentleman, a hard man but a fair man. “Kindness to incompetents seldom provided a dividend,” he wrote after the war “whereas severity invariably paid. As [German Field Marshal Erwin] Rommel said, ‘The best form of welfare is hard training.’ … But the sailor will never admit it.” Gretton had no need as yet to purge this group, however, and the men of B7 seemed to have welded into a tautly skilled team.

Group B7 finally got its blooding in early April when it relieved a Canadian group escorting the fast (nine knots) Convoy HX.231 from New York to the United Kingdom. Entering the mid-Atlantic Air Gap on 4 April, B7 soon had more than enough U-boat contact to make up for its sterile months, as for over four days and nights it battled a pack of fourteen boats. HMS Tay, commanded by Lieutenant-Commander Robert Evan Sherwood, R.N.R., made asdic contact with one of them, U-635, and sank her with a well-placed pattern of depth charges. Another boat, U-632, had been sunk earlier by a RAF Coastal Command Liberator aircraft from Iceland. And U-294, badly damaged by depth charges, was forced to return to base. But six merchantmen were lost in the exchange: three in convoy and three stragglers.

The first loss, that of the British motorship Shillong, was the worst for Gretton. Loaded with zinc concentrate and wheat in bulk, the 5,529-GRT vessel sank from view within two minutes of being torpedoed, casting her entire crew into the sea. On her search for the U-boat, HMS Tay passed slowly through the bobbing survivors, their life jackets aglow with red lights. Gretton shouted encouragement to them, but knew that pursuing the U-boat was his most urgent duty, lest others be attacked, and that Tay must not lie hove to lest a torpedo remove her from the screen. But, as late as 1964, when he wrote about the men he left to die, he called the moment “my most painful memory of the war…. ”

Finally, a mist descended on the ocean swells and ruined the visibility of the U-boats. On 7 April aircraft roared overhead in great numbers. Eventually, landfall was made off the north coast of Ireland, and B7 reentered its home port at Londonderry. Ninety-five percent of the convoy had come through the pack battle unharmed, and B7 had acquitted itself well in its first real trial of pluck and mind. Gretton was pleased—except with the performance of Loosestrife, whose Captain, in his view, had not shaped up to standards, and whom he promptly replaced.

Waiting for Gretton was the recommissioned HMS Duncan, which not only gave him a destroyer to go with the frigate HMS Tay, but also gave him a second HF/DF set (Type FH4), which made possible cross-cut bearings in combination with HMS Tay’s FH3, which alone during HX.231 had proved “worth its weight in gold.” HMS Duncan was also reequipped with the latest asdics, Type 271 10-centimeter radar, and radio transmitters and receivers. On deck she mounted two guns, two torpedoes, and the new forward-firing impact-fused “Hedgehog.” Extra depth charge stowage had been created. His complement of 175 officers and men was unknown and untried, however, and he immediately set them to work jousting with last war-type submarines in the Londonderry exercise area, except on those days when he was asked to review HX.231 with Admiral Horton (CinCWA) in Liverpool, address a large audience of officers on the same operation, and huddle with RAF Coastal Command pilots on how better surface and air escort cooperation might be promoted.

Then came the date, long predetermined, for ONS.5.


As he pulled alongside the Commodore’s ship, Rena, Gretton exchanged documents with Brook, whose orders had come from the Trade Division of the Admiralty, and advised him by loud-hailer of the disposition of his forces. Gretton stationed Duncan in the center behind Argon and formed up the rest of his force on the port bow, beam, and quarter, and on the starboard bow and quarter, with the tanker and rescue trawlers astern. The screen in place, Brook signaled his convoy to gather way on course 280°. Notwithstanding the confidence B7 had gained from HX.231, Gretton had every reason at this moment to be apprehensive. He was sailing northwestward into what forecasters told him was atrocious weather with gale-force winds. That meant that his convoy ships, light on the water because they were in ballast, would be buffeted about like so many champagne corks, and that would work havoc with stationkeeping, throw some ships out of control, and leave others stragglers. Maintaining seven and a half knots would be impossible under those conditions. Furthermore, their course, northwest to 61°45’N, 29°II‘W, a position east of Ivigtut on Greenland, and thence southwest along the Great Banks of Newfoundland, would engage his fleet with pack ice and bergs.

Gretton knew that Western Approaches thought that the northern route was worth the hazard, since aircraft could provide cover south and to the west. Even so, while bombers could fly along much of his route from bases in Northern Ireland and Iceland, ONS.5 eventually would enter the Air Gap longitudes below Greenland that most of those aircraft could not reach. And that was where he assumed the majority of U-boats would be lurking. Were they perhaps already stationed directly athwart his course? Western Approaches had assured him that it had routed ONS.5 through waters that were least expected to be U-boat-infested. It may have informed him, furthermore—the surviving records do not say—that Admiral Donitz had a record number of boats at sea (27 on return passage) and that probably as many as 36 boats were formed into two operational patrol lines, Meise and Specht (Woodpecker), positioned along an arc 500 miles east of Newfoundland.

It could not give him the source of these data because Gretton, like other commanders of his duty and rank, was not “indoctrinated,” that is, in the know about “Z,” or “Special Intelligence,” which was distributed through one-time pad ciphers to a tightly restricted list of recipients in the source-disguising form called “Ultra.” Nor could Western Approaches inform him that the German communications monitoring and cryptographic service, B-Dienst, had possibly discerned ONS.5’s course from decrypts of the Anglo-American Naval Cipher No. 3 (“Convoy Code”). If that was so, it is not known on exactly what day such information might have been communicated to BdU. B-Service messages to BdU no longer exist. Weekly summaries of B-Service information do exist, in the Bundesarchiv-Militararchiv in Freiburg im Breisgau, but the summary for the week of 19–25 April contains no mention of ONS.5. Decryptions of the convoy code were not always current.

An example of the time lag between interception and decryption is the mention of ONS.5 that occurs in the Weekly Summary of 10–16 May, which begins: “The Iceland detachment of ONS.5 consisting of at least three merchant ships [escorted by H.M.S. Vidette] was to leave port at 0715 hours on 23 April in order to rendezvous with the main body [of the convoy] during the daytime of 26 April…. ” Obviously, with such a delay this information had no operational value. The first mention of ONS.5 in the weekly summaries dates from 26 April-2 May, and relates to Third Escort Group (EG3), which will be considered below.

The first week of the voyage went about as Gretton expected. There was the usual mechanical mishap. At 2200 on the first night, the Polish Modlin (3,569 GRT), beset by engine trouble, parted company with the eighth column and returned to the Clyde. At daybreak on the 23rd the weather worsened. High waves and strong winds forced numerous ships out of position. B7 busied itself chivvying stragglers back into line all that day and night. As much as he could, HMS Duncan kept to the center column, No. 6, and maintained the convoy’s slow speed as a means of saving fuel, since the refitted destroyer had been improved in every way except in fuel consumption, for which she was notorious. Her daily consumption at slowest possible speed was 8 percent. At 1630 on the 24th, despite continued heavy seas, HMS Duncan closed with British Lady in an attempt to top up his bunkers, but after the tanker discharged only two of her 600 tons the buoyant wire and rubber hose streamed astern parted, and HMS Duncan had to withdraw and wait for calmer seas. Refueling from Argon was impossible, he discovered, except in mirror-flat water, since the positioning of the American oiler’s canvas hoses would require HMS Duncan to come alongside—too dangerous a maneuver in high seas. The uselessness of Argons precious cargo was foreboding.

HMS Duncan and HMS Tay made regular HF/DF sweeps for U-boats transmitting to BdU or to other boats, but heard nothing. Actually, there was a U-boat not far ahead on their course, but for some reason, still unclear, it had not made a transmission to BdU since sortieing from Kiel, Germany, on 15 April. B7 would not learn of its presence until later in the evening of the 24th, when the boat was attacked by Boeing Flying Fortress “D” of No. 206 Squadron based at Benbecula in the Outer Hebrides. RAF Flying Officer Robert Leonard Cowey was piloting eight miles northwest of ONS.5 on a plan devised by Coastal Command to give the convoy cover from the afternoon of the 24th to midnight on the 27th.

At 1725 one of his crew sighted a fully surfaced U-boat ten miles distant. It was U-710, a newly commissioned Type VIIC, on her first war cruise, under an untried commander, Oblt.z.S. Dietrich von Carlowitz, who was probably unaware of the convoy’s proximity. Instead of alarm-diving at the appearance of Cowey’s aircraft, which was normal U-boat behavior, Carlowitz sent a crew to man the anti-aircraft guns on the platform aft the tower. Inaccurate tracers brushed by as Cowey dove the four-engine bomber to the deck and released a stick of six depth charges (D/Cs) that straddled the U-boat at right angles to her track. The brand-new bows heaved vertically from the explosions and the rear gunner watched the hull of U-Boat sink stern-down in a froth of debris. Cowey circled back and dropped another stick into the wreckage, after which he counted twenty-five survivors flailing in the water. There was nothing anyone could do for them. Low on fuel, and his home base closed in by weather, Cowey headed for Reykjavik. Allies drew first blood from Germans in battle of ONS 5.

For ONS.5, dawn broke on the 25th with the ocean surface in a state of upheaval. Commander Brook struggled to keep his ships in station as howling winds and fierce wave action forced numerous vessels out of line. Brook recorded: “Convoy making 2–3 knots, steering badly.” These conditions continued into the night when, at one point, Brook and Gretton could see seven different sets of “two red lights vertical” from ships that were Not Under Control. The inevitable happened, as HMS Duncan signaled Western Approaches: DURING GALE LAST NIGHT NO. 93 BORNHOLM COLLIDED WITH NO. 104 BERKEL. BOTH DAMAGED 104 IS CONTINUING BUT BORNHOLM LEFT UNESCORTED FOR REYKJAVIK AT 1400. The collision occurred at 2355 when the convoy was proceeding at no more than 2 knots on course 301°. Brook, who did not learn of the accident until the next morning, reported that Bornholm was holed in the Engine Room about 10 feet above the waterline. He commented that progress made against the stormy seas that night was so slight that the convoy was “to all intents and purposes hove-to.”

A moderate gale continued through the morning hours of the 26th, when all ships were sighted but scattered. B7 managed to whip in all but No. 81, Penhale, lead ship of column 8, which straggled astern so badly Gretton detached her to Reykjavik, escorted by Northern Spray. During the forenoon hours convoy speed was 3 knots. At 1400 Gretton was cheered by the arrival of the Iceland contingent—B/s second destroyer, HMS Vidette, with the British Bosworth, the Norwegian Gudvor, and the empty U.S. naval tanker Sapelo—which had been homed to ONS.5’s position by HF/DF and an RAF PBY Catalina. HMS Vidette gave Gretton a destroyer not only faster (25 knots) than HMS Duncan but the twenty-five-year-old V&;W (Long-Range Escorts) Class vessel also had “longer legs,” owing to the removal of one of her boilers and the installation in the vacated space of extra oil stowage. HMS Vidette was equipped with asdic and Type 271 radar, though not with HF/DF; hence she could not join HMS Duncan and HMS Tay in acquiring cross-bearings on U-boat transmissions. Gretton continued to fret about HMS Duncans ability to continue at sea. Unless the weather cleared, he signaled Western Approaches, he might have to separate and refuel in Greenland.

Fortunately, the seas subsided the following morning, long enough for HMS Duncan to top up successfully from British Lady, completing the process at 1100. He was followed by HMS Vidette and the corvette HMS Loosestrife, while RAF Hudsons from Iceland provided cover overhead. Later that day Northern Spray rejoined the convoy. Gretton recorded his position as 61°25’N, 23°49’W, south of Reykjavik and due east of Cape Discord on Greenland. So far there had been no sightings or electronic detections of U-boats. Except for the boat sunk three days before by Fortress “D,” there seemed to be no boats around. If there were, perhaps they were concentrated on a mid-Atlantic convoy known to be on the reciprocal of the same northern course that swept the southern tip of Greenland: The heavily laden SC.128, which departed Halifax on 25 April for the United Kingdom, had been routed to pass north and west of the U-boat groups known to the OIC Tracking Room as of its sailing date.

Between the 22nd and the 25th the Specht and Meise groups, together with new U-boats just arrived in the area, had been reshaped by BdU to form three Groups: Specht, Meise, and Amsel (Blackbird). The Specht line, with seventeen U-boats, ran from 54°15’N, 43°15’W to 51°15’N, 38°55’W. An augmented Meise line, with thirty boats, ran from 59°15’N, 32°36’W to 56°45’N, 28°12’W. The Amsel line, with eleven boats, ran from 54°51’N, 32°00’W to 53°45’N, 29°35’W.12 The BdU orders establishing these dispositions originated as part of a plan to catch westbound ONS.4, but that convoy arrived at New York safely and intact. Two other convoys on northern courses, SC.127 (departed Halifax 16 April) and ON.179 (departed Liverpool 18 April) successfully eluded the patrol lines, SC.127 being diverted to a more northerly course on the 26th after the order enlarging Meise was decrypted nearly fourteen hours after its interception13—and just under the wire, as will be shown below. Convoy ON.180 (departed Liverpool 24 April), which trailed ONS.5, similarly would evade the patrol lines. With the majority of U-boats in northern latitudes, two other U.K.-bound convoys that were at sea in this period, HX.235 and HX.236, were safely directed along southerly courses.

Two entries in the BdU war diary for this period are significant for revealing German operational failures and intelligence misjudgments. The first entry, dated 25 April: An earlier eastbound convoy, HX.234, which sailed the northern route and made port in the U.K. with two ships sunk and one damaged, had been pursued for four days (21–25 April) by no fewer than nineteen boats. The investment of that much energy and time had yielded disproportionately small success. In explaining the failure, Admiral Donitz and Chief of Staff Godt enumerated unfavorable weather, particularly snow and fog; changing visibility conditions; the shortness of the nights on the northern route; strong air cover from Greenland and Iceland; and (cited twice) “the inexperience of the large number of new Commanders who were not equal to the situation.”

The second entry, dated 27 April: the BdU reflected on the fact that on the day before, convoy SC.127 had suddenly changed to a more northerly heading and had passed untouched through a temporary seam between Groups Meise and Specht, which at the moment were maneuvering to new positions. Furthermore, an intercepted American U-boat Situation Report revealed that the Allies knew exactly where the U-boat groups were deployed as well as their current movements, and had the capability to reroute convoys accordingly. How had the enemy gained such knowledge? The BdU answered: “This confirms, more than ever, the suspicion that the enemy has at his disposal a radar device especially effective in aircraft, which our boats are powerless to intercept.”

Of course, it is true that the Allies had 10-centimeter airborne radar, undetectable by any equipment with which the U-boats were then supplied, but its average range sweep was fifteen miles, hardly what would be required to descry the positions of even one wolfpack. Apparently Dönitz and Godt more readily believed in the existence of a (for then) preternatural eye in the sky that laid bare anything that moved across thousands of square miles of ocean than that Allied cryptographers had simply done what B-Dienst had done: cracked the other side’s cipher. That commonsense conclusion—a kind of Ockham’s Razor—never swayed BdU’s mind, and Dönitz himself obstinately refused to entertain the likelihood throughout the war and after it. (He similarly refused to believe at this time, as earlier noted, that the Allies possessed shipborne HF/DF capability.) But had he been aware that cryptographic intelligence was the source of the Allies’ uncanny knowledge, Dönitz would have been greatly encouraged by something else that happened on the day that SC.127 slipped past harm’s way: the Allied cryptographers went blind.

At 1200 on 26 April, owing to changes unexpectedly introduced by Berlin in naval Enigma settings, GC&CS and the OIC Submarine Tracking Room abruptly ceased reading U-boat traffic, and would not read it again until the afternoon of 5 May, a critical period in ONS.5’s westward voyage, since it was during those nine days of cryptographic intelligence blackout that Commander Gretton’s convoy would enter the longitudes where U-boat packs were known to be maneuvering in strength. With what Rodger Winn called “no precise information,” the most that he and Patrick Beesly in the Submarine Tracking Room could tell CinCWA Admiral Horton after 26 April was that three U-boat groups were still thought to be “in the general area off Newfoundland.” As Winn wrote later, “Thus [where ONS.5 was concerned] it was not possible to attempt any evasive routing although the convoy had in the first place been routed as far north as possible to avoid U-boats.’ Three westbound convoys earlier in April, ON.178, ONS.3, and ONS.4, also had been routed north by the tip of Greenland, with small losses to the first two and none to the third. Perhaps ONS.5 would be as lucky.

The OIC Tracking Room was not without alternative sources of information, as noted earlier. Wireless transmissions from the U-boats could be DFed by a shore-based HF/DF network that supplied cross-bearings in the Atlantic theater; the U.K. had twenty stations, the U.S. sixteen, and Canada eleven.19 Furthermore, short signals (Kurzsignale) in the old, still readable Hydra cipher (as Heimische Gewässer had been renamed on 1 January 1943) transmitted by Räumboote (motor minesweepers) escorting U-boats in and out of their Baltic and Biscay bases enabled Winn and Beesly to calculate daily the number of boats at sea; and they took into account the fact that by 26 April BdU had three Type XIV tanker and supply boats—Milchkühe—U-487, U-458, and U—461, on station in mid-Atlantic, which could extend the time some of the attack boats, after refueling, could remain on operations. No alternative source, however, could give Winn and Beesly the same confidence that their Main North Atlantic Plotting Table represented actual conditions at sea as that provided, when readable, by crisply accurate “Z,” particularly at those times when U-boat groups were regularly forming, re-forming, or shifting their operational areas.

The consequences for ONS.5 were immediate, and dangerous. Unknown to Winn and Beesly, hence unknown also to Horton and Gretton, on 27 April BdU established Gruppe Star (Starling), consisting of sixteen newly assembled boats, along a north-south patrol line, or “rake,” at 3o°W between latitudes 61°5o’ and 57°oo’N about 420 nautical miles east of Greenland. On the Kriegsmarine grid chart the new patrol line ran from AD 8731 via AK 3523 to AK 0329. The boats were to be in place by 0900 GST on the 28th.20 The line’s northernmost wing just brushed the course of ONS.5. At 0800 on the 28th the convoy was at position 61°45’N, 29°ii’W, turning southwest. By 0800 the next day it would pass through 30°W to 34°51’W.21 Group Star had been created expressly to catch the next westbound ONS convoy departing on the eight-day cycle, which was ONS.5.

Winn and Beesly were unable to recommend evasive routing because the order creating Star, unknown to them, went out the day after GC&CS’s reading of naval Enigma ended. Commander Gretton could not have had that piece of information. Nor could he have known that while GC&CS’s eyes were shut, the eyes of B-Service were still open. The German radio monitoring and cryptographic service was reading, though not always in real time, the Anglo-American Naval Cipher No. 3 used for convoy routing. The encrypted transmissions included the daily Admiralty or USN U-Boat Situation Reports (which should have been another clue to BdU that its own cipher had been compromised).

When data from B-Service on the composition, sailing date, course, and speed of a convoy reached the green baize table in BdU’s situation room in Berlin/Charlottenburg, it was assigned a number. Convoy ONS.5 was assigned No. 33. We do not know the exact form in which information about ONS.5 was first communicated to BdU because that daily or hourly message traffic no longer exists; but the B-Service’s extant summary for 26 April—2 May discusses the convoy by name in connection with both the Third Escort Group (EG3), which will appear as a Support Group for ONS.5 later in this narrative, and a USN U-Boat Situation Report:

“The Third Convoy Escort Group was positioned at 47°2o’N, 50°03’W on 29 April at 2100, course approximately 100°-200°, speed 15 knots, heading toward ONS.5; it should have changed course at 47°oo’W by 11–13 degrees. The American U-Boat Situation Report of 30 April identified up to 20 boats in the general area 59°61’N, 30°43’W as a result of various wireless direction finding methods, and that a few of those boats continue to be positioned near ONS.5.”

From this entry it is not possible to pinpoint the day when ONS.5 was first identified to BdU. The dates given, 29 and 30 April, relate to events reflected on after a week’s decryption effort. Was word of ONS.5 passed to BdU as early as 26 April, when the week began? We may never know the answer. What is known is that in establishing the position of the Star line, the BdU war diary of 27 April stated: “The object of this is the interception of the next ONS convoy at present proceeding in the North…. A slow southwest-bound convoy is expected there on 28 April.” Advantage: Germany.


At 0900 on the 28th, a time when some late-arriving boats were still maneuvering to their Star stations, Oblt.z.S. Ernst von Witzendorff had U—650 on the surface in naval square [qu] AD 8761. Conditions were a moderate sea, wind from the southeast Force 3, and visibility 12 nautical miles. One of the lookouts with binoculars on the conning tower bridge sighted, “Mastspitzenn!” Von Witzendorff wrote in his KTB: “Mastheads sighted. I am closing them to see what we have. It’s a convoy proceeding southwest.” At 0942 he transmitted an Ausgang F. T. (outgoing wireless message) to BdU: CONVOY AD 8758. Seventeen minutes later he sent again: CONVOY STEAMING AT 8–10 NAUTICAL MILES, COURSE 270°. At 1040 Witzendorff was heartened to see another U-boat of Group Star surface a short distance away on the port side. Three minutes later, he received a message from BdU directed to all Star boats: GROUP STAR SHOULD ATTACK ON BASIS OF WITZEN-DORFF’S REPORT. WITZENDORFF IS FREE TO ATTACK AS SOON AS ANOTHER BOAT HAS CONTACT. At 1110 U-650 updated her first report: WESTBOUND CONVOY NOW IS AD 8728, SPEED 8 KNOTS.

The IIIO transmission was picked up and DFed by HMS Duncan and HMS Tay, as well as by escorts supporting eastbound Convoy SC.127, about 60 nautical miles due south of ONS.5.24 Gretton now knew that ONS.5 was being shadowed—but on behalf of how many boats? He sent the corvette HMS Snowflake to search down the bearing for the transmitting U-boat, which Gretton calculated, based on its strong signal, was “close ahead.” Meanwhile, he altered course of the convoy 35 degrees to starboard and maintained 296° until 1600, when he returned to the original course. Snowflakes search was fruitless, as was a ten-mile high-speed sweep ahead of the convoy by HMS Duncan. Visibility declined to three miles.

At 1650 a U-boat signal detected from astern at 085 degrees indicated that the course alteration, which placed ONS.5 north of the Star rake, had been successful, for the time being. HMS Tay hunted down that bearing and HMS Vidette tracked another, but made no contact. Gretton worried that the U-boat shadower was part of a large pack—one wholly unanticipated—and that it would not divide its forces between his convoy and SC.127 but concentrate them solely on him, and at night, when the U-boats had 17–18-knot surface speed. As dusk came he worried, furthermore, that he could expect no help from aircraft. The air escort given ONS.5 from 24 April had been discontinued at midnight on the 27th/28th, since there were no OIC reports of U-boats in the vicinity. The convoy had been sighted in the late afternoon by a distant USN Catalina, but the possibility of air cover this night, if requested, was remote, since Iceland was socked in by weather.

At 1838, as a heavy head sea formed, HMS Duncan DFed a U-boat close on the port bow, bearing 210°. He chased it at maximum speed and ordered HMS Tay to make a parallel search to port. At 1920 HMS Duncans bridge sighted a cloud of spray thrown up around a U-boat’s conning tower, about two miles bearing 146°. Gretton altered course to pursue the boat, but at a range of about 3,000 yards it dived. In the rough sea HMS Duncan’s asdic failed to make contact, but Gretton fired a ten-charge pattern of D/C by plot. HMS Duncan and HMS Tay then carried out operation “Observant” for an hour. Observant was an asdic square search of two-mile sides with the “Datum Point” (contact point) at the center; one of the escorts could either reinforce the square (sometimes called box) or operate within it. Leaving HMS Tay to sit on the submerged boat while the convoy passed, HMS Duncan returned to establish night stations with the convoy at 2130.25The merchantmen, now beginning a southwest leg, were on course 240°, speed 7.5 knots. The wind was freshening from the southeast at 16–20 miles per hour and the sea was rough, with moderate long swell.

Knowing that U-boats preferred to attack down sea, so that spray did not betray their approaches, and knowing, too, from HF/DF that the U-boats were on the port bow beam, and quarter, and astern, Gretton “placed his field” with strength to that side, leaving the starboard bow uncovered. Attack abaft the port beam was most probable. Where the Germans were concerned, by nightfall only four of Star’s other U-boats had rallied to U–650’s reports: U-386, U-378, U-532, and U-528. That more had not assembled on the convoy’s course, despite BdU’s urging to do so, was owed in part to the “hazy weather” and “strong wind” against which the boats “had to struggle during their pursuit of the enemy.” This, at any rate, was the assessment of BdU on 1 May, after all the excuses were in. If only five boats were on the scene by darkness on the 28th, the rest were not unheard from, however, as every Commander made his evening position report to Berlin. The W/T traffic—“like a chattering of magpies”—was DFed in England as well as by B7’s two HF/DF sets.

For Gretton there were two immediate good results from this chatter. In view of the concentration around ONS.5, CinCWA detached destroyer HMS Oribi from the escort of SC.127 and sent her, at 20 knots, to his assistance. And since this convoy was likely to be targeted by the western U-boat packs, when it reached those longitudes a Support Group (EG3) of four Home Fleet destroyers, HMS Offa in command, was ordered to steam out of Newfoundland at 15 knots to meet ONS.28. With those pledges of reinforcement to brace their spirits, Gretton and his Captains prepared for the night battle sure to come.

In an interview conducted fifty years later, Lieutenant [now Sir] Robert Atkinson, R.N.R., Captain of the corvette HMS Pink, remembered the night of 28 April:

“Well, I remember once getting a fantastic signal. I will give you an example—in H.M.S. Pink. We were about a hundred and fifty miles west-southwest of Iceland, approaching Greenland, and there was a moonlight night—going to be a moonlight night, a very nasty night, windy. And we received a signal from the Commander in Chief [Horton]: “You may expect attack from down moon at approximately 0200.” Now they knew and were able to interpret in Whitehall [the Admiralty] the various radio activity and signals by the German U-boats—great activity. They knew where the moon would be and when it would rise and where the U-boats might attack from—he liked a profile. And by the feverish increased activity of the radio signalling, they knew attacks were imminent. Now we didn’t know that, of course, but the fact that we had a signal telling us to be ready for attack about 0200 made all the difference. And Admiral Gretton, who was Commander Gretton then, we were so highly trained he sent a signal round to our escort group, and do you know what that signal said?—one word, “Anticipate,” that’s all he said. Didn’t get excited, and didn’t tell the do this, or not do the other. It wouldn’t have been any good. We were trained; we knew what to do. And do you know what I did? It was about five o’clock, pitch black, windy as hell, and I said, “Hands to tea, six o’clock.” Cleared lower deck and said, “There’s going to be a hell of a battle tonight. I’m not sure how many of us will see daylight. I intend to see it if I can.” So it was up to us.”

The night battle began earlier than Horton, or Atkinson, expected, at exactly 2358 when one of the four Star boats in the sea to port made the first of six attempted attacks that took place between that hour and daybreak on the 29th. Gretton wrote up his report of the action in unadorned telegraphic style:

"The first attempt was made at 2358, when SUNFLOWER on the port bow got an RDF [radar] contact bearing 170°, range 3000 yards. She ran out towards, but the U-Boat dived, and as no A/S [asdic] contact was obtained she dropped two charges and resumed station. TAY was in station by 0300 [29 April] and at 0045 (the second attempt) DUNCAN got an RDF contact bearing 100°—3500 yards and turned to attack. The U-Boat dived at 2500 yards and A/S contact was picked up at 1500 but almost at once lost. I dropped one charge, ran out and back over the firing position and was resuming station when at 0114 (the third attempt) I obtained an RDF contact bearing 296°—2500 yards. I chased at best speed until at 0119 at range 1100 yards, the U-Boat dived and I reduced to operating speed. RDF plot gave U-Boat’s course as 320° and at 0122 A/S contact was obtained on last RDF bearing, her wake was sighted, and an accurate ten-charge Minol [explosive charge] pattern was dropped. At 0130, while running out after this attack another RDF contact was obtained bearing 146°—4800 yards (the fourth attempt). I turned towards, chased and at 0140, the U-Boat dived at range 3000 yards. No A/S contact was obtained so one charge was dropped by plot. The chasing course was into the wind and seaspray was flying mast high and the U-Boat saw us coming earlier than when we had chased down sea.

As I was turning to resume station after this attack, yet another RDF contact was picked up bearing 210°—4000 yards at 0156 (the fifth attempt) and again I turned and chased at best speed. The U-Boat was heading for the convoy at about twelve knots, but at 0204 at range 1500 yards, he dived and I reduced to fifteen knots. At 0203, the ship passed through a patch of oil about fifty yards diameter, so this U-Boat may have been previously damaged. Good A/S contact was obtained and an accurate ten-charge Minol pattern fired. At the moment of the firing, his wake was clearly seen under the port bow. Contact was regained astern, but lost at 800 yds each time I attempted to attack, so that the idea of a hedgehog [impact-fused bombs fired forward] attack had to be abandoned. I dropped two deep charges on him by plot and resumed station at high speed. At 0054, I had ordered TAY to take position R [port quarter] in my absence. I was back in station by 0310, and TAY ordered to resume position S [astern].

SNOWFLAKE in position P [port beam] drove off the sixth attempt, at 0339, sighting a U-Boat on her port bow, range 1100 yards, steering towards the convoy. SNOWFLAKE attacked and fired two ten-charge patterns, a torpedo narrowly missing her in return. By 0348, SNOWFLAKE had dropped astern into the port quarter position so I moved up to the port beam in her place. At 0354, TAY, in position S, gained and attacked a good A/S contact—a possible but unlikely seventh attempt. By then, dawn was starting to break, and at 0416 I ordered day stations, so that ships would have plenty of time to gain bearing into the ahead stations for the expected dawn attack submerged. The night had been a busy one, the convoy unscathed, and I felt that the U-Boats must be discouraged by our night tactics and might try day attack.

It was a good night’s work for Royal Navy B7 escorts, and Gretton was elated. Against what he estimated were “five or six” U-boats the B7 team had performed splendidly. Not a single ship in the convoy had been sunk or damaged. But he was sure that the U-boats had suffered, and he was right: of the four boats that actually participated in the attacks, two, U-386 (Oblt.z.S. Hans-Albrecht Kandler) and U-528 (Oblt.z.S. Georg von Rabenau) were heavily damaged and forced to withdraw to base, though it is not possible to determine whether it was HMS Duncan or one of the corvettes, HMS Sunflower or HMS Snowflake, that was responsible for either or both. The Type VIIC U-386 limped into home port at St.-Nazaire on 2nd May. On the same day, the Type IXC/40 U—528, also struggling to return from what was her first combat patrol, was approaching the Bay of Biscay when she was located , bombed and badly damaged on the surface by a radar equipped Halifax II bomber “D” of 58 Squadron from RAF Coastal Command and then she was finished off by two Royal Navy escort ships , the destroyer HMS Fleetwood and corvette HMS Mignonette, escorting nearby convoy OS.47. Both Royal Navy escort ships were vectored from the convoy to the location of U-528 by Halifax bomber aircraft and they located submerged U-528 with a through sonar sweep and then HMS Fleetwood fatally damaged German U-Boat with a prolonged depth charge attack. When U–528 had to surface to avoid sinking both HMS Fleetwood and HMS Mignonette located , hit and sank her with gunfire with the loss of eleven killed, forty-five captured (picked up by Royal Navy escort vessels) from U-boat. Gretton certainly thought he had a kill on the third U-boat attempt, which he called “an accurate attack,” and this may have caused damage to one of the two boats cited. In any event, it was, as he said, “a most successful night.”

On her maiden escort with the Group, HMS Duncan had detected and attacked four separate U-boat advances in the space of one hour and fifty minutes, and in weather conditions where the ship was pitching and rolling wildly, and seas washing down the quarter deck made the work of loading and reloading the heavy D/Cs both difficult and dangerous. Gretton used the loud-hailer to praise the behavior of his ship’s company during their first baptism of fire. The two corvettes had also given a good account of themselves, although each committed an error: In dropping two D/Cs at 2208 to scare off any U-boats in her vicinity, HMS Sunflower inadvertently dropped a calcium flare that lit up the entire seascape—“rather an unnecessary advertisement,” as her Canadian Captain, Lt.-Cmdr. J. Plomer, R.C.N.V.R., dryly put it. HMS Sunflower turned back to extinguish the light and, on a second attempt, by going hard to starboard, drew it through the propeller stream.

HMS Snowflake had a dicier experience, which Gretton called “an unusual slip in the drill.” During the sixth U-boat attack, HMS Snowflake followed a radar contact at 0332 and sighted an approaching boat in the process of diving. When about 200 yards astern of the boat’s swirl, the wheel was suddenly put hard-a-starboard, though no such order had been given. As a result, the U-boat passed on a reciprocal bearing 200 yards down the port side and no D/Cs were fired. HMS Snowflake’s Captain, Lieutenant Harold G. Chesterman, R.N.R., dropped three D/Cs between the U-boat and the convoy as scare tactics. At 0336 he gained an asdic bearing at range 2,000 yards and turned to the attack. As he did so, at 0338, ship’s hydrophone first detected, then lookouts sighted, a torpedo pass 20 yards down the port side.

This was the only torpedo seen the night of 28th/29th. It was launched by U-532 (Korv. Kapt. Ottoheinrich Junker), but it was not the only eel in the water. Just three minutes before, by periscope, Junker had launched a four-torpedo Fächerschuss (fan shot) from his bow tubes at what he called “the third steamer” in a column, estimated by him at 5,000–6,000 GRT. All the eels missed. The depth of run was three meters, which should have been shallow enough to hit a ship even in ballast. Seven and a half minutes later, Junker would hear end-of-run detonations. Meanwhile, using the two stern tubes that a Type IXC/40 boat commanded, he got off a double launch against HMS Snowflake (only one of which torpedoes was sighted), missing again, as already noted, and hearing end-of-run detonations seven minutes later.

Junker states in his KTB (war diary) that as he placed the escort in his crosshairs, he could see convoy steamers in the background. His six misses in that crowded seascape were perhaps ineptitude, or just bad luck. The fault could not have been inexperience: the thirty-eight-year-old native of Freiburg im Breisgau had commanded U-boats since 1936, though it bears mention that he did not have a single ship to his credit. With U-532 having to reload all tubes, the initiative now passed to HMS Snowflake, which Junker’s periscope displayed steaming toward him at high speed, only 1,200 meters distant. “Alarm!” his KTB records, as U-532 opened flood valves and dived to greater depth—and just in time, as HMS Snowflake dropped a ten-charge pattern over him at 0343. When the noise and turbulence subsided at 0345, HMS Snowflake regained asdic contact. With the recorder marking well, Chesterman came round to port, and at 0351 fired a ten-charge pattern set to 100 and 225 feet. This second attack, Chesterman noted, “is considered to be accurate.” Then, with only “doubtful” asdic contact showing on the recorder, and concerned that he should husband his D/Cs remaining for battles to come, Chesterman shaped course to rejoin the convoy.


Deeper than 225 feet, U—532 was still alive, but wounded. Junker wrote in his KTB:

“The entire hull of the boat vibrated violently. Before each depth-charge series we could hear the asdic sound pulses [Ping-tongg! Ping-tongg!]…. We found major damage done to the forward hydroplanes. They ran quite laboriously and made strong knocking noises. They tended to stick in the “hard up” position, but could be freed again. For the time being we are limiting them to “up 15°“…. A large number of manometers, lamps, and electrical equipment have gone out, though without any restrictive effect on the boat’s operation…. Battery array No. 1 was badly cracked, with the result that acid leaked into the bilges…. The magnetic compass broke, which is a nuisance because, unable to use the noisy gyrocompass when in creep, or stalking speed [Schleichfahrt, about 2.5 knots] we have no means for checking the course of the boat…. I don’t want to end up running into the hands of the enemy.”

Junker records that he remained submerged, experiencing or hearing various series of D/Cs—five more ten-patterns—“additional series or single drops”—“new depth charge attacks”—“three more series”—as far as 0140 (2340 GMT on the 29th) on 30 April, when he surfaced, the last hours having been spent breathing through potash cartridges because of the 3 percent level of CO2 in the boat. Troubled by intolerable noises inside the boat, he set course back to base. The BdU gave U-532 credit for “two hits” and duly noted the boat’s ordeal: “She was hunted for fifteen hours.” The problem with the fifteen-hour story is that the D/Cs heard by U-532 after HMS Snowflake s two drops were not meant for her but for the U-boat involved in the McKeesport event, described below. The sum of U—532’s patrol was: no hits, six misses, and one badly bent boat forced back to base.

The BdU did not learn of U-532’s alleged hits until 2 May. At the time of the night battle it was dismayed that not a single Treffer, or hit, had been scored. In rationalizing the failure, it argued first that the boat’s messages to Berlin were inaccurate. They overestimated the convoy’s speed—certainly that was the case with U-650’s initial estimates—and the reports from U-386 and U—378 on the enemy’s position were too far distant from each other to make any sense. Second, atmospheric or magnetic interference apparently was preventing BdU’s operational orders from getting through, since no acknowledgments were coming back, and no messages of any kind were received from the boats during the period from 0300 GST on the 29th to 1200 on the 30th. Third, Force 6 winds, heavy seas, and limited visibility greatly hampered surface operations.36 For the first time in a long while, Admiral Dönitz’s command and control system had been frustrated and bootless on the night of the 28th/29th. But an enterprising individual commander, operating on his own initiative, could break the string.

In the early daylight of the 29th, fulfilling Gretton’s expectation that, unable to overcome B7’s night tactics, the U-boats might try submerged attacks in daytime, U—258 (Kptlt. Wilhelm von Mässenhausen) slipped inside and under the convoy formation, where he took a position at periscope depth starboard of the convoy’s No. 4 column. In doing so, he somehow avoided the asdic sweeps by the escorts on day stations as well as by Tay, which was searching astern for damaged or shadowing boats, and by Vidette, which returned to her station at 0725 after searching out 15 miles. It was broad daylight. At exactly 0729 1/2, the furtive U—258 scored a hit on the 6,198-GRT American Moore-McCormack freighter McKeesport, ship No. 42, the second ship in No. 4 column, which was on a return voyage from having delivered to Manchester, England, a cargo of grain, steel tanks, foodstuffs, and chemicals.

Gretton was asleep in his sea cabin when the alarm bell rang. Dashing to the bridge, he ordered “Artichoke” at 0730. In this operation the ship in position “S,” astern, closes the torpedoed ship at maximum asdic speed, and ships in the “forward line,” that is, “A,” ahead, “B,” starboard bow, and “L,” port bow, turn immediately outward to a course reciprocal to the course of the convoy and sweep in line abreast at 15 knots or at the maximum asdic sweeping speed of the slowest ship, the wing ships passing just outside the convoy wake, the inner ship(s) between the columns of the convoy, until reaching a line 6,000 yards astern of the position the convoy was in when the ship was torpedoed. All other escorts continue on the course of the convoy.

Five minutes later, Gretton saw a torpedo, which had passed through several columns without a hit, explode at the end of its run on the convoy’s port quarter, indicating an attack from starboard, probably along 180 degrees. The rescue trawler Northern Gem acquired an asdic contact astern of McKeesport and made an attack with three D/Cs. There was no result. And an “Observant” carried out by Duncan proved fruitless. Admiringly, Gretton called U—258’s action “a bold effort,” and, what was more, the attacker got away—for now.

On board McKeesport the torpedo’s explosion had come as a complete surprise. The Chief Officer, Junior Third Officer, and two seamen-lookouts on the bridge made no periscope sighting. Neither did the U.S. Naval Armed Guard who manned a four-inch gun on the afterdeck. Nor did the seaman-lookout on the fo’c’s’le, although on the starboard side he did see a long, dark, round object leap across a trough of the choppy sea, which he thought was a fish. He correctly identified a second torpedo that ran astern, but it was too late to warn about the first. When the warhead detonated with an awesome bang, it not only shook the whole ship; it opened a hole at the collision bulkhead of No. 1 hold, which, like holds 2, 3, and 5, was filled with sand ballast; put the steering apparatus out of order; flooded the forepart up to tween decks; and twisted plates, beams, and hatches. Fire spread through wooden grain fittings, but the inrushing sea put it out.

McKeesport lurched to port, causing the British Baron Graham on that side to consider evasive action. Incredibly, the listing merchantman maintained convoy speed in her station for fifty minutes, until, with her engine room flooding, she started to sink at 0815, and the Master ordered Abandon Ship. Life nets were thrown over the side and the boats were lowered. Unfortunately, the boats became entangled in the nets, and so did some of the men who used them to climb down to rafts. Several seamen fell into the water, one of whom would later die from exposure, the only fatality from McKeesport’s complement. Last to leave were the Master and the crew of the Naval Armed Guard, under command of Ensign Irving H. Smith, U.S.N.R., who gallantly stood by their gun until ordered to leave. The rescue ship Northern Gem came alongside and picked up the survivors: forty-three seamen, one critically injured, and twenty-five naval crew.

While the Master had cast overside his Confidential Books, including his codes, in a weighted container, he had neglected to jettison his ship’s log and charts, on which future rendezvous positions were marked. Accordingly, Northern Gem made an effort to sink McKeesport with her ship’s gun, but the derelict ship remained afloat. It was U.S. Navy Department policy, stated by Secretary of the Navy Frank Knox on 30 March 1942, that “no U.S. Flag merchant ship be permitted to fall into the hands of the enemy.” Since that was the policy and McKeesport could be boarded by a U-boat crew, Gretton ordered HMS Tay to go back and hole the wreck, which she did with depth charges.

The steel shell went down with all her relics of human habitation, including eight decks of playing cards and other games: cribbage, dominoes, checkers and acey deucy, as well as sports equipment: darts, deck tennis, two pairs of boxing gloves, and one medicine ball; and divertissements: one portable radio, one Victrola, and twelve records. The Master had no complaint about his escorts. The sinking was, he said, “just one of those things.” HMS Tay then pursued a U-boat contact 49 miles astern and did not rejoin B7 until 0600 the next day, the 30th. At 1100 that morning the convoy half-masted colors for the burial at sea of McKeesport’s lone fatality, John A. Anderson, a Swedish national, who had died on board Northern Gem.

No attack on ONS.5 developed during the night of the 29th/30th April, although HF/DF and asdic contacts led HMS Duncan and HMS Snowflake to drop “scare tactic” charges. The destroyer HMS Oribi, homed from astern by HF/DF, arrived during the night, at 0100, from EG3. In the southwesterly wind and sea she had only been able to make II knots.40 Her HF/DF equipment (Type FH3) lent additional detection ability to the screen. Coastal Command, alerted to ONS.5’s peril on the 28th but delayed by weather conditions at 120 Squadron’s air base at Reykjavik, finally was able to reestablish air contact when a VLR Liberator arrived overhead the convoy at 0645 on the morning of the 30th. Soon afterward, however, owing to a drop in visibility, the aircraft returned to base in Iceland.

The U-boats would remain at bay all that morning, and at 1045, the short-legged HMS Oribi took advantage of the respite to oil from British Lady. Unfortunately, the destroyer, which was unaccustomed to refueling at sea, fouled the oiler’s gear. That fact, plus a new deterioration in the weather that had already been, in Gretton’s words, “astonishing even in the North Atlantic,” made it impossible for other escorts to top up—with ultimately grave consequences for HMS Duncan. By 2100 another gale was blowing from ahead, the wave heights were rising steeply, and the escorts were rolling gunwales under.

At 0105, in the first highly visible sign that some of the U-boats had maintained contact during the past forty-one hours, HMS Snowflake acquired a U-boat’s radar signature at 3,300 yards, ran down the bearing, fired a starshell at about 10 o’clock three miles from convoy, sighted the boat at 3,000 yards, fired “near misses” at her with both the four-inch deck gun and 20mm Oerlikon anti-aircraft (AA) guns at maximum depression, and forced it to dive. To discourage it further, HMS Snowflake dropped a D/C on the swirl—which was a hazardous thing to do given the rough sea, which prevented an attacking ship from getting much beyond the blast effect—as HMS Duncan discovered himself when he dropped two on another contact at 2345: with maximum speed up sea only 8 to 9 knots, the D/C pressure waves lifted his stern clean out of the water, opened leaks, and, what was worse, smashed all the gin glasses in the wardroom. There were two other “scare tactic” D/C drops that night, and no general attack on the convoy developed.

The morning weather on 1 May was atrocious. By afternoon a Force 10 gale was dead in the convoy’s teeth, preventing all but the most modest progress forward. Convoy speed was 2.7 knots and dropping. In the tempest, columns as well as ships within columns separated from each other. Commodore Brook’s log noted: “Half convoy not under command, hove to and very scattered.” Gretton, whose Duncan was hove to with winds pushing alternately against one bow and then the other, marveled that an entire convoy could be brought to virtually stationary condition. On Pink, Lt. Atkinson placed a chair on the raised platform at the fore part of his open bridge and went into half-sleep, rocking with the motion of the corvette. Nearby were a gyro compass and voice pipes to helmsman and navigator. Compass repeaters were on both wings port and starboard. Ahead and several feet below was the asdic hut (or office). Aft and a deck lower was the helmsman. On the port quarter of the bridge was the tall radar hut (office, house). Aft of the bridge were the ship’s mast and funnel. For protection against the cold gale Atkinson wore a heavy sweater, a cloth, not very warm, duffel coat with hood, a Balaclava helmet (knitted wool head sock), naval cap, seaboot stockings, and mitts. Like the rest of the crew, he was the recipient of wool clothing articles knitted by women volunteers in Australia, New Zealand, and Canada, with whom correspondence was exchanged and lifelong friendships forged.

Aircraft flew over the dispersed merchantmen during the day, including two RAF VLR Liberators from 120 Squadron in Iceland who gave valuable assistance by identifying the positions of stragglers, and by warning of icebergs, growlers, and pack ice starting thirty miles ahead. Less helpful were two U.S. Army B-25 Mitchell bombers from Ivigtut, Greenland, which made no contact whatever with the convoy either by wireless (W/T), voice radio (R/T), or light signals (V/S), although one of them, as Gretton learned later, made an unsuccessful attack on a U-boat some 60 miles to the south; and one of them further helped to confuse BdU by forgetting to switch off its navigation lights: The flashing beacons, which, of course, announced the bomber’s position and course to any U-boat that might be watching, caught the attention of U-381 (Kptlt. Graff Pückler), which at once signaled BdU about an apparent secret weapon. In Berlin, where Grossadmiral Dönitz and Konteradmiral Godt were at this time unusually accommodating of the notion of secret devices, the BdU war diary for 1 May noted: “The [U-351] observed what was probably a new type of location gear. The Commander repeatedly noticed planes approaching at great height and carrying a light like a planet that went on and off.”

What is more interesting to learn from the 1 May diary entries concerning convoy “No. 33” is that BdU decided that with only six of sixteen Star boats reporting contact with the convoy, the rest having failed to gain purchase, with three survivors of those six now submerged to avoid both the weather and the aircraft, and with so little to show for four days’ effort, further pursuit of ONS.5 was not worth the candle. At dusk the longwave antenna array at Calbe, 43 kilometers south of Magdeburg, sent the order, which could be heard by the submerged boats to a depth of 25 meters: break off the operation. BdU’s rationalization of the failure read: “This attack failed only because of the bad weather, not because of the enemy’s defenses.” No doubt a different appreciation of the battle was entertained on the bridge of HMS Duncan.


By dawn the next day, the weather had moderated somewhat, and the speed of the convoy was back up to 5 knots. During the previous twenty-four hours only 20 miles had been made. Gretton and his escorts took advantage of the settling seas to round up stragglers, of whom there were many, some at a distance of 30 miles from the Commodore. In this B7 and HMS Oribi were helped by a VLR Liberator from the Reykjavik squadron that flew over 1,000 miles to assist in locating ships. Eventually, most of the flock was gathered, except for two parties taken under charge by HMS Pink and HMS Tay some miles astern, and two laggards that peeled off to sail independently. In the forenoon of 2 May, Gretton and Brook began negotiating the first ice pack on their route. Small growlers and floes now became the hazard rather than high seas. HMS Duncan thought this a good time to top up from British Lady, but the oiler’s constant alteration of course to avoid the ice made the maneuver impossible; and by the time ONS.5 was clear of ice the wind and sea were making up again from the west-southwest, frustrating Gretton once more.

In the evening B7’s transmitters vectored in the EG3 Support Group destroyers of Home Fleet, HMS Offa, HMS Penn, HMS Panther, and HMS Impulsive, which joined at 2040. Unfortunately, like HMS Oribi, these were all short-legged ships that had expended a good amount of their fuel making rendezvous. Gretton’s HMS Vidette was the only destroyer in the enlarged screen that had been designed for or, as was the case, modified for long-range escort duty. There was a brief awkward moment when Gretton, who was junior in rank to the Support Group senior officer, Captain J. A. McCoy, R.N., in HMS Offa, “made requests of” (gave orders to) his senior in grade; but Gretton found McCoy more than willing to accept the subservient role, and very friendly in his cooperation.

That night McCoy’s ships took up extended screen stations assigned to them by Gretton, which changed from first dark to midnight, from midnight to dawn, and from daybreak to sunset. There was no sign of the enemy during the night, and the morning of 3 May was similarly quiet, except that gale-force winds from the southwest continued to howl around the main body of the convoy, which now numbered thirty-two ships together. The close escort and support ships spent the forenoon searching for stragglers.

Gretton exempted himself from that labor and crawled ahead at convoy speed, anxious about his fuel remaining, and deciding what to do about it. Because of the still heavy seas, topping up from British Lady was out of the question; and the weather forecast did not allow for any calmer surface ahead. What oil he had left in his bunkers was sufficient to make Newfoundland only at economical speed. If he stayed with the convoy, the likelihood was that he would go dry and have to be towed. If the enemy was still in touch, his powerless ship would invite easy attack. As for transferring his command of B7 to another ship and sending HMS Duncan and her crew to St. John’s, that, too, was not an option: the appalling weather made transfer by boat or jackstay impossible. So HMS Duncan would have to go, and Gretton with her—at a time, he grieved, when ONS.5 was still in jeopardy, and just at the beginning of a story that Gretton later would describe as “probably the most stirring of convoy history.”

At 1600, by R/T, he handed over command as Senior Officer Escort to Lt.-Cmdr. Robert Evan Sherwood in Tay, changed course, and proceeded at best economical speed, which was 8 knots, toward St. John’s. Though emotionally depressed—“thoroughly ashamed of ourselves,” he would say—Gretton understood rationally that the reason for his withdrawal lay not with any inadequacy of himself or his crew, but with the Royal Navy strategists and engineers who decided in the 1920s what ought to be the fuel endurance of a destroyer. In fact, that night and the next morning three destroyers of the Support Group similarly left the convoy because of fuel depletion, first HMS Impulsive to Iceland, then HMS Panther and HMS Penn to Newfoundland. Also, on the 4th, Sherwood detached Northern Gem with her McKeesport survivors to Newfoundland. And at the same time, he signaled CinCWA that unless the weather cleared enough to make oiling from U.S.S. Argon practicable, he would have to detach destroyers HMS Offa and HMS Oribi no later than Wednesday morning the 5th.

Helped by unexpectedly fine weather and a boost from the Labrador Current, a disappointed HMS Duncan made St. John’s with four percent of fuel remaining. Left behind in the sea lanes was a severely diminished convoy escort with four of its once seven-strong destroyer force already removed from the screen, facing now the threat that it would lose two more destroyers on the morrow. That would leave ONS.5’s escort a predominantly corvette force. And at just this juncture HMS Tay’s asdic went out and was pronounced irreparable.

But the new commander Sherwood had at least three reasons for optimism: for one thing, CinCWA ordered First Escort (Support) Group at St. John’s, consisting of the Egret class sloop HMS Pelican; Commander Godfrey N. Brewer, R.N., Senior Officer; the River Class frigates HMS Wear, HMS Jed, and HMS Spey; and the ex-U.S. Coast Guard Lake class cutter HMS Sennen, to “Proceed at best speed through position 47 North 47 West and thence to reinforce ONS.5”; for another, the winds subsided to Force 6 and the seas abated somewhat, with the result that convoy speed advanced during a twenty-four-hour period from 3 to 6 knots; and, for still another, ONS.5 incredibly had passed through most of the dreaded Greenland Air Gap without sustaining a single attack.

Yet 4 May was a day when lifted spirits also had their troughs: HF/DF receptions, which had been for a while still, became active again and gradually increased in number, indicating to Sherwood that U-boats, whether from the last group or from a new one, were reacquiring contact from port bow and beam. Convoy ONS.5 was not yet beyond jeopardy.

Sherwood’s credentials for leadership were longstanding and well-tested. At sea since 1922, when he served with the Merchant Navy, he joined the Royal Naval Reserve in 1929, became a sublieutenant in minesweepers, and served nine months on the battleship HMS Warspite. While continuing a member of the reserves, he resumed Merchant Navy duties with Holyhead-Dublin steamers until the outbreak of war, when he took an asdic course, spent a short stint with the Dover Patrol, and transferred to corvettes, assuming command in 1940 of HMS Bluebell, among whose fifty-two-man crew he found only three or four who were “capable of any real action of any kind at all.” In time he trained them to a high degree of seamanship and technical proficiency, and of himself he said that it was good training to have held command early of a vessel as difficult to handle as a “Flower” class corvette, a ship type that struggled against every wave and swell. HMS Bluebell, he said, “would do everything except turn over.” Advanced to command of HMS Tay in 1942, he was assigned to Gretton’s escort group, with which he captained the first ship on which B7’s Senior Officer Escort embarked.

Described as being of medium height and stocky build, Sherwood framed bright, humorous eyes within a full naval beard. Not very well spoken, one of his fellow Captains said of him, and lacking in the kind of presence that Gretton generated, he was nonetheless a fine seaman whose command decisions were swift and firm. Though he was a reservist and lower ranking than Gretton, the Support Group regulars accepted his orders. On every fighting bridge there was confidence that Sherwood had mastered Gretton’s painstaking game plan of search and sink. Now, as ONS.5 groped toward the unknown, with HF/DF contacts growing more numerous, and with all the original B7 group that remained damaged and worn by bitter weather and a running fight, it would take all of that mastery to see the convoy into port. Sherwood’s concern would have been all the greater had he known that fewer than 70 nautical miles dead ahead as large a wolfpack as any of the war would assemble to meet him.



The Battle for ONS.5

And two things have altered not
Since first the world began—
The beauty of the wild green earth
And the bravery of man


THE DESTROYER, WITH ITS SPEED, armament, maneuverability, and capacity to keep the sea, was the traditional and deadly enemy of the submarine. The even better ASW vessel, the destroyer escort, was not yet available in numbers from American yards, where volume construction began in April. Much good could be said as well for the performance to date of the “River” class frigate (301’6” long overall, displacing 1,370 tons, speed 20 knots) and the “Black Swan” class sloop (299 feet long overall, displacing 1,300 tons, speed 19¼, knots). But the surprise of the ASW war was the smaller and relatively slow “Flower” class corvette (205 to 208 feet long, displacing 950 to 1,015 tons, speed 16 knots). These perhaps most famous of British ships of the war—fame engendered in great part by the fictional corvette Compass Rose in Nicholas Monsarrat’s novel The Cruel Sea—owed their name to World War I “Flower” class sloops that were based on a whale-catcher design and used in that conflict for minesweeper and utility duty.

Their namesake successors, produced originally by the same yard, Smith’s Dock Company at Middlesbrough, and designed by the same naval architect, William Reed, were produced, beginning in 1939, for minesweeping and ASW work in the North Sea and Channel. Their immediate ancestor was Reed’s and Smith’s Dock Company’s commercial whaler Southern Pride, whose specifications were closely followed, though somewhat enlarged, because of that craft’s ability to keep the sea. In adapting for naval use an already existing mercantile vessel design, and one that was simple to construct, the Admiralty ensured that the new single-screw “Flower” class “corvettes,” as they were to be known, could be produced in non-naval yards throughout the U.K. Altogether 221 “Flowers” and “Modified Flowers” would be built in Great Britain and Canada. (Only one “Flower” exists at the date of this writing: HMCS Sackville, launched in 1941, which helped to escort convoy ON.184 during the fateful month of May 1943; fully restored, she is on display at the Bedford Institute of Oceanography , Nova Scotia)

Corvettes, which, as Monsarrat wrote, “would roll on wet grass,” were not designed for deep ocean work, but that, ironically, became their primary service as Britain desperately sought escorts for her trade lifeline, and “Flowers” accompanied all but one of the non-carrier-escorted HX, ON, ONS, and SC convoys that crossed the northern sea lanes during the months of April and May. Though well proven as seaworthy in midocean escort, the corvettes’ lively dipping and wallowing in heavy seas placed a pronounced strain on ships’ companies. Said seaman Cyril Stephens of HMS Orchis: “Sick … yes, that was the first baptism of a corvette…. It was like a corkscrew. About the third dip and you’d get tons and tons of water come over the fo’c’s’le…. You had wet clothes on steam pipes trying to dry, you had water floating around all over the place, people being sick…. It was awful.”

Not restricted to courses that headed into heavy seas, to avoid damage or capsizing, as was the case with built-for-speed destroyers, the corvettes could show their broad beams to hard seas with ease and confidence. Not given to slamming, either, as destroyers were want to do in sea states of 5 and upward, the early short-forecastle corvettes did pitch and heave violently, and it was the resulting vertical acceleration that caused seasickness—in combination with poor ventilation, a dank ambiance, and the unbalanced diet of RN messing. As naval architect David K. Brown pointed out recently, vertical acceleration, which varied linearly with wave height, also led in its severe phases to impaired judgment and performance, hence impaired fighting effectiveness (although Sir Robert Atkinson, who commanded Pink, told the writer that he experienced no such adverse mental effects). In an attempt to resolve that problem, later ships of the original class were given a lengthened forecastle deck, extra sheer and flare to the bows, and various bridge improvements. The short length of the corvette had one advantage, and that was a small turning circle, assisted by a good-size rudder in the propeller wash, that enabled the ship to get her stern quickly over a submerged U-boat contact.

The number of D/Cs carried on board increased during the war from twenty-five to fifty. Crew numbers similarly increased, from twenty-nine to over eighty. Endurance was rated at 3,850 miles at 12 knots on 233 tons of fuel, the average convoy run being 3,000 miles, though actual endurance was uniformly less. Throughout the war corvettes appeared in the so-called Western Approaches camouflage scheme, which was an all-white ship that merged with the skyline, on which were painted panels of light sea blue or light sea green that blended with the sea. The flower names that adorned these vessels occasioned some ribaldry among seamen in larger RN ships, but no one could doubt the stamina, fighting spirit, or comradeship of the men who sailed in them.

Howard O. Goldsmith was Leading Sick Berth Attendant on HMS Snowflake:

“I suppose the nearest thing we ever came to was on ONS.5. We had probably the worst trip weather-wise of any…. There were times there when the convoy was literally stationary because some of the merchant ships just couldn’t make headway against the wind and the sea. And although the engines were turning, the screws were turning, we were just sitting there stationary. And to give you an idea of what it was like, the upper deck was out of bounds. The skipper put the upper deck completely out of bounds. The only people allowed above decks were the bridge crew, and they were told to use the Captain’s companionway, which was inboard, to get to the bridge, otherwise out of bounds completely. This seaman was a Newfoundlander who’d been brought up on schooners, and he said, “Well you don’t get weather like this every day. I’m going up the mast, see what it’s like.” And he did, he went to the top of the mast in that sea, right to the cross trees, above the crow’s nest. And when he came down he said when we were in the trough he couldn’t see over the top of the waves. So he was talking, what, seventy foot waves, that’s big. And we had this for the whole trip…. The damage to the ship was incredible. People don’t realise the tremendous power of the sea, unless you’ve seen what it can do. But I mean, for instance, all the fo’c’s’le stanchions, which were inch-thick iron stanchions, carrying the guard wires round the fo’c’s’le, they were all bent at right angles to the deck. They’d just been as though a giant hammer had hammered them over to a right angle. One ship’s boat had completely disappeared. One was stoved in. Just the waves had stoved it in, smashed it in. We used to have meat lockers which were welded to the deck. They were on the upper deck to keep the meat fresh, no fridges, you see, and they were welded on the deck and to a superstructure above the deck, welded top and bottom, with wire mesh sides to them, so that the air could flow through, and after that storm, not only had they gone, all the meat had gone, and there were just the weld spots on the deck and above, that’s all that was left. That’s just the force of the wind, the force of the sea, carried all that away. Deck lockers that were bolted and welded down just disappeared, just went, we never saw them go. Incredible power”

What now if the power of wind and seas, which B7 and ONS.5 thus far had managed to survive, was replaced by the power of a U-boat armada the size and threat of which were as formidable as any in the history of submarine warfare? At the same time that Sherwood and his convoy were edging past what was left of the Air Gap, Dönitz and Godt, prompted by the failure of Gruppe Star, were ratcheting up the offensive by combining Stars boats with those of the western Group Specht.5 Indeed, Star’s thirteen boats, including some replacements (U-7/0 having been sunk, and U-386, U-528, and U-532 having withdrawn with damage), proceeded south-southwest through the Air Gap alongside and past ONS.5, to the convoy’s east. BdU’s original intent was to have Star join Specht’s seventeen boats in stalking eastbound Convoy SC.128 (BdU’s convoy No. 34), which had departed Halifax on 25 April and was steaming on a northerly course to the west of Specht. On 1 May U—628 had reported smoke clouds that BdU took to be from SC.128. Specht-was directed to chase it down, but it could not do so. It is possible that what U-628 sighted was not SC.128 but the EG3 Support Group on its passage to join ONS.5.

By 1800 on 3 May the new Specht-Star rake ran from 56°21’N, 44°35’W (on the German grid AJ 5333) to 54°57, 39°35’W (AK 4449). Boats from this formation reported seeing smoke clouds and starshells; one signaled it had been driven off by a destroyer. The supposition in Berlin was that these boats were in contact again with SC.128. With a note of frustration, if not desperation, BdU signaled: DO NOT HOLD BACK…. SOMETHING CAN AND MUST BE ACHIEVED WITH 31 BOATS. Berlin estimated that the convoy was steaming on a course between 20° and 50°. But it was not. While some of its escorts took a course northeastward, firing starshells to draw off the U-boats, SC.128, alerted to Specht-Star s estimated position by Canadian Naval Service Headquarters, Ottawa, which had DFed it, took a jog to the west before resuming a northerly course and then turning east above the north end of the rake. Successfully evading Specht-Star, the convoy would arrive at Liverpool on 13 May without mishap. In breaking off the hunt, BdU noted, “Most of the boats are short of fuel, and it is pointless for them to run about after the convoy.”

At the same time BdU formed Specht-Star it also augmented Gruppe Amsel, to the south, and formed it into four subgroups, I, II, III, and IV, of five U-boats each, except for I, which had six. Amsel now ran, with gaps between the subgroups, from 51°51’N, 49°05’W (AJ 7933) to 44°15’N, 39°35’W (BC 9646). In a revealing comment about BdU’s awareness of the Allies’ shore-based HF/DF capability, the Berlin war diary observed: “This new type of disposition should avoid the drawbacks that arise when a patrol remains in one place for a long time so that it is D/Fed, sighted, located, etc. by the enemy, who thus finds out its entire extent.” The boats at the extreme ends of this segmented line were supplied with dummy F.T. messages with which to create the impression of a larger line “stretching right around the Newfoundland Banks.” That impression was not unlikely to be made, since the OIC Tracking Room was now estimating the number of U-boats at sea to be 128, the highest ever known, representing nearly 60 percent of the Atlantic operational force. When the Allies DFed the boats forming Amsel, Dönitz and Godt expected they would discover the gaps and attempt to vector convoys through them. The plan then was to combine the subgroups into a closed line. Before it had a chance to work, however, that plan was overtaken by a new plan, as BdU realized, on 4 May, that the Amsel boats would be needed in operations to the north.

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