page_title: Imperial Japanese Navy in World War II
section_title: Submarines
hierarchical_section_title: Imperial Japanese Navy in World War II / Submarines
context_page_description: The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the third most powerful navy in the world, and the naval air service was one of the most potent air forces in the world. During the first six months of the war, the Imperial Japanese Navy enjoyed spectacular success inflicting heavy defeats on Allied forces, being undefeated in every battle. The attack on Pearl Harbor crippled the battleships of the US Pacific Fleet, while Allied navies were devastated during Japan's conquest of Southeast Asia. Japanese naval aircraft were also responsible for the sinkings of HMS Prince of Wales and HMS Repulse which was the first time that capital ships were sunk by aerial attack while underway. In April 1942, the Indian Ocean raid drove the Royal Navy from South East Asia. After these successes, the Japanese now concentrated on the elimination and neutralization of strategic points from where the Allies could launch counteroffensives against Japan's conquests. However, at Coral Sea the Japanese were forced to abandon their attempts to isolate Australia while the defeat at Midway saw them forced on the defensive.
context_section_description: Japan had by far the most varied fleet of submarines of World War II, including manned torpedoes (Kaiten), midget submarines (Ko-hyoteki, Kairyu), medium-range submarines, purpose-built supply submarines (many for use by the Army), long-range fleet submarines (many of which carried an aircraft), submarines with the highest submerged speeds of the conflict (Senkou I-201), and submarines that could carry multiple bombers (World War II's largest submarine, the Sentoku I-400). These submarines were also equipped with the most advanced torpedo of the conflict, the Type 95 torpedo, a 533 mm (21 in) version of the famous 610 mm (24 in) Type 93.
  A plane from one such long-range fleet submarine, I-25, conducted the only aerial bombing attack on the continental United States when Warrant Flying Officer Nobuo Fujita attempted to start massive forest fires in the Pacific Northwest outside the town of Brookings, Oregon on September 9, 1942. Other submarines undertook trans-oceanic yanagi missions to German-occupied Europe, such as I-30, I-8, I-34, I-29 and I-52, in one case flying a Japanese seaplane over France in a propaganda coup. In May 1942, Type A midget submarines were used in the attack on Sydney Harbour and the Battle of Madagascar.
  Overall however, Japanese submarines were relatively unsuccessful. They were often used in offensive roles against warships (in accordance with Mahanian doctrine), which were fast, maneuverable and well-defended compared to merchant ships. In 1942, Japanese submarines managed to sink two fleet carriers (Yorktown and Wasp), one cruiser (Juneau), and a few destroyers and other warships, and damage several others (aircraft carrier Saratoga). They were not able to sustain these results afterwards, as Allied fleets were reinforced and started using better anti-submarine tactics including those learned from the Battle of the Atlantic. By the end of the war, submarines were instead often used to transport supplies to island garrisons. During the war, Japan managed to sink about 1 million tons of merchant shipping (170 ships) with her 184 submarines, compared to 1.5 million tons for Britain (493 ships), 4.65 million tons for the US (1079 ships) and 14.5 million tons for Germany (2,000 ships) with 1,000 U-Boats.
  Early models were not very maneuverable under water, could not dive very deep, and lacked radar. Later in the war, units fitted with radar were in some instances sunk due to the ability of US radar sets to detect their emissions. For example, USS Batfish sank three such in the span of four days. After the end of the conflict, several of Japan's most innovative and advanced submarines were sent to Hawaii for inspection in "Operation Road's End" (I-400, I-401, I-201 and I-203) before being scuttled by the U.S. Navy in 1946 when the Soviets demanded access to the submarines as well.
caption: An Imperial Japanese Navy I-400-class submarine, the largest submarine type of World War II
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