With the success the Germans were have with their U-Boats against Merchant Shipping, why did the Japan not use their submarines in a similar fashion?

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I believe Japanese submarine doctrine was to go after the other Navy. They did not show themselves to be very flexible.


Also it should be noted, that the Pacific Ocean is vast. Much so compared to Atlantis. And as already stated above, Japanese doctrine was different than Germans focusing on fleet vs. fleet action.


Wasn’t it interesting that the American submarine doctrine very much emulated the Germans?

Damm crappy torpedoes!


After the war spoiler Japanese commanders were interrogated by the Americans. After being shown what they should have done by the Americans, they were frankly embarrassed.

Imo Japan did a few things against its own interest in WWII

  1. It should have has a worLd-leading combined forces doctrine between the Army and the Navy.

  2. A profound emphasis on convoy protection and escort.

  3. A world class emphasis on logistics and supply 8n operations, especially for such a remote area.

They failed on all three counts.


Unlike the Atlantic where there was an established convoy and travel route the Pacific was more complicated as it is literally dotted with thousands of islands and the area is vast and convoys were impractical per se. Add to that Japanese doctrine in war was very inflexible with enemy navies as the primary target as the Japanese saw them as the primary threat. Add to that the Japanese were quite spread out and had a lot of places to defend and my understanding is the Japanese used their impressive sub fleet mainly in defense rather than offense.


Excellent points. Japan should have done all the Americans ended up doing. Japan could not even move their goods in peacetime and were dependent of other nations merchant ships. This did not bode well for war.

At the end of the days the competition and dislike between Army and Navy was so destructive to their efforts.


Also the German strategy was to starve Britian by closing all kind of food supplies. The same strategy would in no way work against US. The traffic in the Pacific was almost military and that meant much less shipping . The Japanese strategy was never a war of attrision over supplies


Good point there were no huge civilian/military shipping convoys in the Pacific with the exception of:

The lend lease convoys to Vladivostok, but according to Weinberg there was a tacit agreement that Japan would not touch those in exchange for the Soviets not allowing US bombers on Soviet soil (Siberia and Japan are really close).

There was just less opportunity and sinking US transports between e.g. Hawaii and LA would eat into Japans fuel supplies. Fuel was short as these lovely oil fields they captured couldn’t be moved to Japan! :stuck_out_tongue_closed_eyes: :stuck_out_tongue_closed_eyes: :stuck_out_tongue_closed_eyes: :expressionless: :smiling_imp:



The primary purpose of submarines in Japanese naval doctrine was reconnaissance. The IJN submarines were also considered the primary atrictional units of the Imperial Japanese Navy. So they were only allowed to engage when they sighted and had a favorable opportunity to torpedo a heavy cruiser, battle cruiser, aircraft carrier, or battleship. The IJN considered the loss of a submarine in exchange for the torpedoing of a heavy cruiser or aircraft carrier to be an acceptible trade off.

So the vast majority of imperial submarines are assigned to 6th Fleet (Submarine Fleet until August 1943, afterwards Advanced Expeditionary Force) with only a couple of submarine divisions consisting of two to four submarines being assigned to the area fleets like 4th Fleet (Mandates) or 8th (South Seas).

Under IJN doctrine, 6th Fleet would deploy 16 to 36 submarines 72 to 96 hours before Combined Fleet sorties forming a reconnaissance line moving in advance of Combined Fleet to radio back any contact of enemy forces. Once the submarines reached the area that Combined Fleet estimated that the enemy forces are deployed in, the submarines would form one or two picket lines with each submarine being assigned a search box to radio back the location of enemy naval units along with sightings of enemy planes and what direction they are flying in. The picket line or lines would be altered as Combined Fleet picked up more intelligence about the location of enemy forces allowing for opportunistic strikes against enemy heavy warships.

At this point in the war, the sortying of 6th Fleet was the primary indicator that Combined Fleet was being committed to a major offensive against Allied forces so this is what Allied Intelligence is specifically looking for when radio direction finding of the IJN warships and decryption of IJN codes.

Finally, there is nothing wrong with the Picket Line doctrine. As the number of American submaries are increased in the Pacific, the US Navy will also use picket lines with far more effectiveness against the IJN as well as using the line for pilot rescue. Carrier pilots are given the location of the picket line so they know exactly where to bail out if their planes are too damaged to return to the carrier so they can be rescued by American submarines. The problem with Japanese doctrine is that they do no use their submarines for anything else at this period of the war.