Allied submarines in the Pacific War
They were mass produced without adequate testing during development, leaving four major engineering faults and only a 20% success rate from December 1941 to late 1943.
[citation needed] Pre-war U.S. Navy doctrine—like that of all major navies—specified that the main role of submarines was to support the surface fleet by conducting reconnaissance and attacking large enemy warships.
Merchant ships were regarded as secondary targets, and the circumstances in which they could be attacked were greatly limited by prize rules set out in the London Naval Treaty, to which the U.S. was a signatory.
The U.S. Navy built large submarines which boasted long range, a relatively fast cruising speed and a heavy armament of torpedoes.
[citation needed] The submarines' commanders and crewmen were considered elite and enjoyed a strong esprit de corps.
[13][14] Throughout the war, Japan was dependent on sea transport to provide adequate resources, including food, to the home islands and supply its military at garrisons across the Pacific.
[22] Japanese destroyers formed the bulk of convoy protection; they had impressive night fighting capabilities, but had deficiencies in sonar and radar compared to equivalents of other navies.
Signals intelligence broke the "maru code" in January 1943, after a gaffe by U.S. Customs pre-war had caused Japan to change it,[25] and American aircraft engaged in aerial minelaying in Operation Starvation.
[28] In a break with pre-war doctrine (which, like Japan's, had presumed a rush across the Pacific and a "decisive battle" between battleships),[29] with the London Naval Treaty, and with long-standing U.S. defense of freedom of the seas, U.S. naval commanders in the Pacific were ordered by the U.S. Navy Chief of Staff to "execute unrestricted air and submarine warfare against Japan" on the afternoon of 7 December 1941, six hours after the Japanese attack.
[30] This order authorized all U.S. submarines in the Pacific to attack and sink any warship, commercial vessel, or civilian passenger ship flying the Japanese flag, without warning.
[33] Due to inadequate prewar planning, which made no provision for defensive minelaying,[34] nor for placing submarines on station around the Philippines,[35] nor off enemy harbors,[36] the Asiatic Fleet's efforts to counter the Japanese invasion of the Philippines were unsuccessful and the fleet's surviving submarines were forced to withdraw to Surabaya in the Dutch East Indies (DEI).
[39] Following the fall of the DEI, only a handful of British and Dutch submarines were based in the Indian Ocean, and these had little impact on Japanese forces in the area.
At the Battle of Midway, although the attack on the battleship Kirishima by USS Nautilus had been unsuccessful, it drew the destroyer Arashi temporarily away from the main fleet to drop depth charges, and the destroyer's return was traced by USS Enterprise's VB-6 to the Japanese task force, where the dive bombers promptly set on fire the fleet carriers Akagi and Kaga.
As a result of several key improvements the previous year, U.S. submarines inflicted tremendous losses to the heavy units of the Imperial Japanese Navy in 1944.
The British Eastern Fleet was responsible for submarine operations in the Bay of Bengal, Strait of Malacca as far as Singapore, and the western coast of Sumatra to the Equator.
[48] The submarines were deployed to conduct reconnaissance, interdict Japanese supplies travelling to Burma, and attack U-boats operating from Penang.
By March 1945, British boats had gained control of the Strait of Malacca, preventing any supplies from reaching the Japanese forces in Burma by sea.
The submarine HMS Trenchant torpedoed and sank the heavy cruiser Ashigara in the Bangka Strait, taking down some 1,200 Japanese army troops.
This resulted in the loss of thousands of Japanese troops, who were being transported to bolster Japan's already declining manpower on land in the final years of the war.
This included taking photos of areas of interest (such as potential beaches for amphibious landings), and reporting on the movements of IJN warships.
[63] In late 1944 and 1945 several submarines were fitted with a newly developed FM (frequency modulated) sonar that was intended for detection of submerged mines, first Tinosa and Spadefish, and later Flying Fish, Skate, Bonefish, Crevalle, and Sea Dog.
[65] British and Dutch submarines also landed and supplied special forces troops, rescued airmen, and shelled shore installations on nine occasions.
The Fourteenth Flotilla, which was equipped with six XE-class submarines, arrived in Australia in April 1945 but was almost disbanded in May as no suitable targets could be found.
The Flotilla's fortunes improved in early June, however, when undersea telegraph lines in the South China Sea were identified as being worthwhile targets along with a heavy cruiser at Singapore.
