Submarines of the Imperial Japanese Navy
Imperial Japanese Navy (IJN) submarines formed by far the most varied fleet of submarines of World War II, including manned torpedoes ("Kaiten"), midget submarines ("Kō-hyōteki", ), 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" ), and submarines able to carry multiple bombers (World War II's largest submarine, the Sentoku ). They were also equipped with the most advanced torpedo of the conflict, the oxygen-fuelled Type 95 (which are sometimes confused with the famed Type 93 Long Lance torpedo).
Japanese submarine I-55 (1925)
The four Kaidai Type 3a vessels were the first mass-produced Japanese fleet submarines. Based largely on the indigenous Kaidai Type II ("I-52") a strengthened double hull, their design was also influenced by the largest of the German submarines in Japanese hands, the SM U-125. The hull had almost the same outer dimensions as the "I-52", but the increased thickness of the inner hull permitted a diving depth of 60 meters. Internal volume was slightly increased by making the hull slightly trapezoidal in cross-section, at the expense of 300 tons of additional displacement. External differences included an anti-submarine net cutter on the bow, as well as an O-ring for towing purposes.