Allied submarines in the Pacific War
Allied submarines were used extensively during the Pacific War and were a key contributor to the defeat of the Empire of Japan.
During the war, submarines of the United States Navy were responsible for 56% of Japan's merchant marine losses; other Allied navies added to the toll.[1] The war against shipping was the single most decisive factor in the collapse of the Japanese economy. Allied submarines also sank a large number of Imperial Japanese Army (IJA) troop transports, killing many thousands of Japanese soldiers and hampering the deployment of IJA reinforcements during the battles on the Pacific islands.
They also conducted reconnaissance patrols, landed special forces and guerrilla troops and performed search and rescue tasks.[2] The majority of the submarines involved were from the U.S. Navy, with the British Royal Navy committing the second largest number of boats and the Royal Netherlands Navy contributing smaller numbers of boats.
The Allied submarine campaign is one of the least-publicized feats in military history,[1] in large part because of the efforts of Allied governments to ensure their own submarines' actions were not reported in the media. The U.S. Navy adopted an official policy of unrestricted submarine warfare, and it appears the policy was executed without the knowledge or prior consent of the government.[3] The London Naval Treaty, to which the U.S. was signatory,[4] required submarines to abide by prize rules (commonly known as "cruiser rules"). It did not prohibit arming merchantmen,[5] but arming them, or having them report contact with submarines (or raiders), made them de facto naval auxiliaries and removed the protection of the cruiser rules.[6] This made restrictions on submarines effectively moot.[5]
A major reason why the U.S. submarine campaign is little known is the defective Mark 14 and Mark 15 torpedoes. 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. For those two years U.S. submarines struggled to sink any Japanese warships or merchant ships. For example, during the 1941-42 Philippines campaign the United States Navy's Asiatic Fleet's 23 modern state-of-the-art submarines failed to sink a single Japanese warship even when scoring direct hits, because the torpedoes all failed to explode for myriad reasons.[7][8]
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. Before the war, Japan estimated the nation required 5,900,000 long tons (6,000,000 t) of shipping to maintain the domestic economy and military during a major war. At the time of the attack on Pearl Harbor Japan's shipping capacity was much greater than that, totaling 7,600,000 long tons (7,700,000 t) of shipping: the Japanese merchant fleet was capable of 6,400,000 long tons (6,500,000 t), and smaller craft were capable of an additional 1,200,000 long tons (1,200,000 t).[15]
At the start of the war, the U.S. submarine fleet was ineffective, for multiple reasons:[16]
Despite an awareness that shipping was vital, the Japanese military seriously underestimated the (eventual) threat from Allied submarines. This overconfidence was reinforced by the ineffectiveness of Allied submarines in the early part of the war.[21] Anti-submarine warfare was accorded a low priority and few warships and aircraft were allocated to protecting merchant shipping.[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.[23] Moreover, Japanese Navy doctrine in relation to commerce defense was very bad.[24]
The size and effectiveness of the Allied submarine force increased greatly during the Pacific War. The U.S. increased production of modern submarines from 1942 onward. The efforts of Admiral Charles A. Lockwood were crucial for the rectification of the Mark 14's problems (which were nevertheless not resolved until September 1943).[16] He also selected more aggressive submarine skippers. 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. As a result of all of these developments, U.S. submarines inflicted devastating losses on Japanese merchant shipping in 1943 and 1944, and by January 1945 had effectively destroyed the Japanese merchant fleet.[26]
Poor torpedoes claimed at least two U.S. submarines[27] out of 48 lost on patrol.[28]
Post-war[edit]
Allied actions in the Pacific are believed to have been a mitigating factor in reducing the sentence of Großadmiral Karl Dönitz following the Nuremberg Trials, who was accused of similar actions in the Battle of the Atlantic; indeed, Admiral Nimitz provided Dönitz with a statement saying his boats behaved no differently.[66] The official judgment of the International Military Tribunal cited the statement as part of the reason Dönitz's sentence was "not assessed on the ground of his breaches of the international law of submarine warfare."[67]