Allied submarines in the Pacific War
On the afternoon of the 7th of December 1941, six hours after the Japanese attack on Pearl Harbor, U.S. Navy Chief of Staff issued a directive to Pacific commanders. The order authorized all submarines in the region to execute unrestricted air and submarine warfare against Japan without warning. This policy allowed crews to sink any warship, commercial vessel, or civilian passenger ship flying the Japanese flag. Thomas C. Hart, commander in chief of the U.S. Asiatic Fleet, issued the same order at 03:45 Manila time on his own initiative. He knew that Harold Stark intended to do so as well. The London Naval Treaty had previously required submarines to abide by prize rules, but this new directive removed those restrictions entirely. The United States adopted an official policy of unrestricted submarine warfare that appears to have been executed without prior government consent.
A major reason why the U.S. submarine campaign remained little known was the defective Mark 14 torpedo. These weapons were mass produced without adequate testing during development, leaving four major engineering faults. From December 1941 to late 1943, only a 20% success rate existed for these torpedoes. 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. The torpedoes all failed to explode for myriad reasons. Poor training led to an excessive reliance on sonar, and skippers exhibited undue fear of destroyers' sonar and aircraft. Admiral Charles A. Lockwood selected more aggressive submarine skippers to counter these issues. His efforts were crucial for the rectification of the Mark 14's problems, which were nevertheless not resolved until September 1943.
Allied submarines sank around 1,300 Japanese merchant ships by the end of the war in August 1945. By that time, the Japanese merchant marine had less than a quarter of the tonnage it possessed in December 1941. Japan estimated the nation required 6 million tons 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 totaled 7 million tons. Smaller craft were capable of an additional 1 million tons. Overall, U.S. Navy submarines sank roughly 200 warships as well. Despite the need to maintain sea lanes for its empire, the Japanese never successfully developed a cost-effective destroyer escort better suited for convoy duties. It also did not have the industrial might to replace the losses of its heavily armed destroyers or ill-protected merchantmen.
U.S. submarines inflicted tremendous losses to the heavy units of the Imperial Japanese Navy in 1944. They destroyed the Japanese fleet carriers Shōkaku and Zuikaku in the Battle of the Philippine Sea. Three Takao-class cruisers were sunk or disabled at the start of the Battle of Leyte Gulf. Also sunk that year were the battleship Musashi, which remains the only Japanese battleship lost to a submarine. Escort carriers Shin'yō, Taiyō, and Un'yō fell to Allied torpedoes. The fleet carrier Shinano was the largest vessel ever sunk by a submarine. In total, Allied submarines sank around 1,300 Japanese merchant ships and roughly 200 warships. These actions collapsed the enemy economy and hampered the deployment of IJA reinforcements during battles on Pacific islands.
From early 1944 U.S. submarines rescued crews of aircraft forced down over the ocean. By the end of the war, submarines had rescued 504 airmen including George H. W. Bush who later became the 41st President of the United States. American submarine Nautilus landed Marine Raiders for an abortive raid on Makin Atoll. This drew Japanese attention to weak defenses which were strengthened when the U.S. invaded the atoll in November 1943. British and Dutch submarines also landed special forces troops and shelled shore installations on nine occasions. Britain deployed a flotilla of midget submarines called XE-class to conduct sabotage raids. On the 31st of July, XE4 cut the submerged Singapore-Saigon telegraph cable near Cape St. Jacques in French Indochina.
The British Eastern Fleet was responsible for submarine operations in the Bay of Bengal and Strait of Malacca as far as Singapore. Few large Japanese cargo ships operated in this area, so British submarines targeted small craft operating in inshore waters. The Eastern Fleet's submarine force continued to expand during 1944. By October 1944 it had sunk a cruiser, three submarines, six small naval vessels, 200,000 tons of merchant ships, and nearly 100 small vessels. Three British submarines were sunk by the Japanese during the war: HMS Trenchant, HMS Thetis, and HMS Porpoise. In April 1945, the 8th Flotilla moved to Subic Bay in the Philippines while the 4th Flotilla replaced it at Fremantle. At that time, there were 38 British and Dutch submarines in the theater with five more boats on their way from Europe.
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Common questions
When did the United States adopt unrestricted submarine warfare against Japan?
The United States adopted an official policy of unrestricted submarine warfare on the 7th of December 1941. U.S. Navy Chief of Staff issued a directive to Pacific commanders six hours after the Japanese attack on Pearl Harbor authorizing all submarines in the region to execute air and submarine warfare without warning.
Why were early U.S. torpedoes ineffective during World War II?
Early U.S. torpedoes failed due to four major engineering faults in the Mark 14 model that were mass produced without adequate testing. From December 1941 to late 1943, these weapons achieved only a 20% success rate because they often failed to explode despite scoring direct hits.
How many Japanese merchant ships did Allied submarines sink by August 1945?
Allied submarines sank around 1,300 Japanese merchant ships by the end of the war in August 1945. This destruction reduced the Japanese merchant marine to less than a quarter of its tonnage from December 1941 when capacity totaled 7 million tons.
Which battleship was lost to a submarine during the Pacific War?
The battleship Musashi remains the only Japanese battleship lost to a submarine during the conflict. It was sunk alongside other heavy units like fleet carriers Shōkaku and Shinano which was the largest vessel ever sunk by a submarine.
Who was rescued by American submarines during World War II?
American submarines rescued 504 airmen including George H. W. Bush who later became the 41st President of the United States. These rescues began in early 1944 when U.S. submarines started saving crews of aircraft forced down over the ocean.