Submarines of The Imperial Japanese Navy - World War II

World War II

Imperial Japanese Navy submarines formed 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 used by the Imperial Japanese Army, see Type 3), fleet submarines (many of which carried an aircraft), submarines with the highest submerged speeds of the conflict (Sentaka I-200), and submarines able to carry multiple bombers (World War II's largest submarine, the Sentoku I-400). They were also equipped with the most advanced torpedo of the conflict, the oxygen-fuelled Type 95, sometimes confused with the type 93 Long Lance torpedo. A plane launched from one such fleet submarine, I-25, conducted what remains the only aerial bombing attack on the continental United States, when Warrant Flying Officer Nobuo Fujita piloting a Yokosuka E14Y scouting plane dropped four 168-pound bombs in an attempt to start forest fires outside the town of Brookings, Oregon, on September 9, 1942. In February 1942, the submarine I-17 fired a number of shells from her deck gun at the Elwood Oil Fields near Santa Barbara, California. None of the shells caused any serious damage.

Overall, despite their technical innovation, Japanese submarines were built in small numbers and had less effect on the war than those of the other major navies. The IJN pursued the doctrine of guerre d'escadre (fleet vs fleet warfare), and consequently submarines were often used in offensive roles against warships, which were fast, maneuverable and well-defended compared to merchant ships. During the Battle of Midway, I-168 administered the coup de grace to USS Yorktown (CV-5), as well as sinking the destroyer USS Hammann (DD-412). Later in 1942, Japanese submarine I-19 sank the fleet carrier USS Wasp (CV-7), damaged the battleship USS North Carolina (BB-55), and damaged the destroyer USS O'Brien (DD-415) (which sank later on 19 October 1942) with a single salvo of torpedoes. However, as fuel oil diminished and air superiority was lost, Imperial submarines were no longer able to continue with such successes. Once the United States was able to increase its production of destroyers and destroyer escorts, as well as bringing over highly effective anti-submarine techniques learned during the Battle of the Atlantic, they continually took more and more of a toll on Imperial Japanese submarines, which also tended to be slower and not as deeply-diving as their Kriegsmarine counterparts. The Imperial Japanese Navy's doctrine of fleet warfare (guerre d'escadre) resulted in its submarines seldom posing a threat to allied merchant convoys and shipping lanes to the degree that the Kriegsmarine's U-boats did as they pursued commerce raiding against Allied and neutral merchant ships.

During the last two years of the War in the Pacific, the IJN submarines instead were often used to transport supplies to isolated island garrisons—ones deliberately bypassed by the Americans and the Australians. During the war, IJN submarines did sink about 1 million tons (GRT) of merchant shipping (184 ships) in the Pacific; by contrast U.S. Navy submarines sank 5.2 million tons (1314 ships) in the same period, while U-boats of the German Navy, the IJN's Axis partner, sank 14.3 million tons (2,840 ships) in the Atlantic and other oceans.

Early models of IJN submarines were not very maneuverable under water, could not dive very deeply, and lacked radar. (Later in the war units that were fitted with radar were in some instances sunk due to the ability of American radar sets to detect their emissions. For example, the USS Batfish sank three such IJN submarines near Japan in just four days). After the end of the conflict, several of Japan's most original 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 Soviet Union demanded to have access to the I.J.N. submarines, also.