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).
Imperial Russian Navy
Due to the ongoing blockade of Port Arthur in 1904, the Imperial Russian Navy dispatched their remaining submarines to Vladivostok, and by the end of 1904 the last of seven subs had reached their new base there. Using the seven boats as a foundation, the Imperial Russian Navy created the world's first operational submarine fleet at Vladivostok on 1 January 1905. On 14 February 1905 the new "submarine fleet" sent out its first combat patrol consisting of the vessels "Som" and "Delfin". With patrols varying from 24 hours to a few days, the sub fleets first enemy contact occurred on 29 April 1905 when Imperial Japanese Navy torpedo boats fired upon "Som", withdrawing after failing to score a hit. On 1 July the Russian submarine "Keta" made contact with two Japanese torpedo boats in the Tartar Strait. "Keta" could not submerge quick enough to obtain a firing position and both adversaries broke contact.