Submarines of the Imperial Japanese Navy
Imperial Japanese Navy submarines originated with the purchase of five Holland type submarines from the United States in 1904. Japanese submarine forces progressively built up strength and expertise, becoming by the beginning of World War II one of the world's most varied and powerful submarine fleets.
History of submarines
Japan had 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 (Sentaka "I-200"), and submarines that could carry multiple aircraft (WWII's largest submarine, the Sentoku "I-400"). These submarines were also equipped with the most advanced torpedo of the conflict, the oxygen-propelled Type 95 (what U.S. historian Samuel E. Morison postwar called "Long Lance").