Although the invasion of Italy followed closely on from the conquest of Sicily and may be regarded historically as a sequel to it, from the point of view of the Grand Strategy of the war there is a great division between the two operations. The conquest of Sicily marked the conclusion of the North African campaigns which cleared the Axis forces from the southern shores of the Mediterranean Sea. The invasion of Italy was part of the next phase of Grand Strategy, which was targeted at removing Germany from the war by way of the cross-Channel invasion. Italy would no longer be high on the priority list for men and matériel; operations here would be subsidiary to the preparations for OVERLORD, and the armies which had been successful in Africa would be broken up and selected divisions would be removed from the Mediterranean theatre and redeployed to the United Kingdom. Those formations that remained to carry out the campaign included many that were understrength or not fully trained or equipped.
The clear break between the Sicilian and Italian campaigns is reflected in the differences in the objectives that the Combined Chiefs of Staff (CCS) had for the two operations. For the former the intention was clear cut and definite - firstly, to make the Mediterranean line of communications more secure; secondly, to divert German pressure from the Soviet front; and thirdly, to intensify pressure on Italy. 2 The possibility of removing the enemy forces which defended Sicily from the Axis order of battle by cutting their escape route to mainland Italy was not seriously attempted. For Italy the CCS informed Eisenhower that the major strike against the Axis would be made in North West Europe, and that he should plan to remove Italy from the war and to tie down the maximum number of German divisions with the purpose of keeping them away from Normandy. Taking Italy out of the war would play its part in this, for Italy had about two million men under arms in some sixty divisions; these were not necessarily first-class troops, but they were deployed in garrisons in southern France (seven divisions) and the Balkans (thirty-two divisions), as well as in many anti-aircraft and coastal defence units in both areas. Their removal would force the Germans to replace them with their own forces, which could now not be employed against OVERLORD.
The CCS also set forth a general pattern of Mediterranean operations for 1943-44, dividing it into three main phases: (1) the elimination of Italy from the war and the establishment of air bases as far north as the Rome area, and, if feasible, including the Ancona area; (2) the capture of Sardinia and Corsica; and (3) the eventual entry of Anglo-American forces and the bulk of the re-equipped French forces into southern France.
The CCS orders to remove Italy from the war could only be achieved by invading the mainland. The intelligence staff believed that capturing Sicily would not be sufficient. Nor would taking Sardinia guarantee Italy’s capitulation - it had to be the mainland itself. In any event, even should Italy surrender once its islands fell, it would be necessary to occupy Italy to prevent the Germans moving into the country in strength. For Alexander the obvious way forward was to invade, and to do so in such a way that the Allied force was as concentrated as possible - the forthcoming withdrawal of formations to the United Kingdom, together with the requirement to tie down yet more for garrison and defensive purposes elsewhere in the Middle East, left the Allies with less than the optimum force levels for Italy; as Alexander pointed out in his report on the campaign, the Allied forces ‘never at any time enjoyed any but the slenderest margin of superiority over the Germans, and usually not even that, and, above all, the invasion of the West was never deprived of any resources in men or materials by the needs of the operations in Italy’. To compound the difficulties, the CCS were unable to define any geographical objectives because the campaign in Italy would be defined by the outcome of Sicily - the factors which would shape the later campaign were not yet clear. The very geography of Italy was ready-made for defence with its long ‘leg’ bearing difficult mountains running down its length, rivers running across its width, and many places where nature could be reinforced to produce defensive lines which would prove to be almost unbreakable. What man had been able to make in the years before the invasion to improve communications by building roads through the mountains could be undone in a matter of less than a day with the aid of modern explosives.
From Alexander’s perspective as commander of 15th Army Group, operations in Italy would be determined by geography - which was ready-made for defence. Where nature had not provided readily defensible positions, the enemy was sure to reinforce their lines by demolishing the communication system which previous generations had striven to put in place. The roads and bridges that had taken years to build could be removed in a matter of hours by explosives, and it would take far longer to replace them in order to facilitate an Allied advance; certainly not swiftly enough to guarantee keeping the Germans on the back foot and unable to construct fresh defences farther back.
On the positive side, the Allies were permitted a measure of flexibility by their amphibious capabilities - so long as they remained available and were not withdrawn for OVERLORD. There was a constraint on their use, however - that of the range of air cover. Having regard to the vulnerability of naval vessels, evidenced by the losses of HMS Prince of Wales and HMS Repulse to Japanese aircraft off Malaya earlier in the war, Alexander was not about to risk a repeat in the Mediterranean. Whereas in the Pacific large numbers of American aircraft carriers were able to provide cover, no such situation pertained in the Mediterranean: carriers were few. The Fleet Air Arm capability could provide a maximum of eighty sorties on the first day of an operation. The sortie numbers dropped each day thereafter, and after three days were negligible. 5 Spitfire range (with 90-gallon tanks) was 180 miles from north-east Sicily, once airfields had been constructed in that region. At the time of planning, the Sicilian operation had not been completed, and there was only one small airstrip known to be available there. The arc of operations drawn from Sicily extended to the island of Capri, just north of Salerno, and included the Italian provinces of Calabria and Basilicata. Nowhere here were any targets of major strategic importance; the area was the poorest in Italy and was one of mountains and difficult communications. Just beyond fighter range were two targets worth taking - the city and port of Naples, and the Italian naval base of Taranto - but a direct assault on either of these heavily defended locations, especially without air cover, was out of the question.
Calabria appeared to be the only route into Italy, with a relatively safe passage across the Straits of Messina, but this way led into a narrow region with mountains rising to 6,000 feet in height, which offered the defender a number of points on which to base his resistance. The danger of focusing- the invasion solely at this point was that the Allies could find themselves stuck in a barren region as winter approached, unable to advance sufficiently far to tie down significant German forces. It was evident to Alexander that an effort must be made to identify somewhere - risky that it might be - at the extremes of fighter cover but closer to strategic objectives. Detailed planning started in Allied Force Headquarters on 3 June 1943, but much would depend upon the progress of the operations in Sicily. The first few days there gave promise for the future: the Italian forces on the island, which might have strongly resisted the landings on their homeland, had little heart for the fight. Many units, especially the coastal defence formations, put up virtually no fight at all, and mass desertions were frequent. The civilian population seemed welcoming, seeing the Allies as liberators. These indications, together with the comparatively light Allied casualties and the limited damage imposed upon the landing craft employed during the invasion, contributed to a more ambitious plan for Italy than would otherwise have been the case.
Fifth Army , A Coalition At War - Ian Blackwell