The Type 3 submergence transport vehicle was a class of transport submarines built for the Imperial Japanese Army during the Second World War. The IJA planned to build over 400 boats, however only 38 boats were completed until the end of war. The IJA called them Maru Yu.
The class consists of four unofficial subclasses resulting from manufacturing differences among the contracted builders. The manufacturer may be discerned by the appearance of the sail.
''Yu 1''-class
Basic model of Yu I type. First boat Yu 1 was prototype of the Yu I type boats. The Hitachi-Kasado Factory built all of the Yu 1-class boats. Their sail was closed.
Yu 7, assigned Detachment 2, Transport Submarine Group in November 1944, survived war.
Yu 8, survived war.
Yu 9, survived war.
Yu 10, assigned Detachment Kuchinotsu, Transport Submarine Group on 15 May 1945, survived war.
Yu 11, assigned Detachment Kuchinotsu, Transport Submarine Group on 15 May 1945, assigned Detachment Mikuriya in June 1945, survived war.
Yu 12, assigned Detachment Kuchinotsu, Transport Submarine Group on 15 May 1945, survived war.
Yu 13, assigned Detachment Mikuriya in June 1945, survived war.
Yu 14, assigned Detachment Kuchinotsu, Transport Submarine Group on 15 May 1945, assigned Detachment Mikuriya in June 1945, survived war.
Yu 16, survived war.
Yu 17, survived war.
Yu 18, survived war.
Yu 19, survived war.
Yu 20, survived war.
Yu 21, survived war.
Yu 22, survived war.
Yu 23, survived war.
Yu 24, survived war.
Yu 25, incomplete until the end of the war.
''Yu 1001''-class
The Japan Steel Works-Kaita Factory built all of the Yu 1001-class boats. They were equipped with an open-top sail.
Yu 1001, launched on 27 March 1944, completed on 15 June 1944, assigned Detachment 2, Transport Submarine Group in November 1944, sunk by air raid at Shimoda on 12 August 1945.
Yu 1002, assigned Detachment 2, Transport Submarine Group on 11 February 1945, survived war.
Yu 1003, assigned Detachment 2, Transport Submarine Group on 11 February 1945, survived war.
Yu 1005, assigned Detachment 2, Transport Submarine Group on 13 February 1945, survived war.
Yu 1006, survived war.
Yu 1007, assigned Detachment Kuchinotsu, Transport Submarine Group on 15 May 1945, assigned Detachment Mikuriya in June 1945, survived war.
Yu 1008, survived war.
Yu 1009, survived war.
Yu 1010, survived war.
Yu 1011, incomplete until the end of the war.
Yu 1012, incomplete until the end of the war.
Yu 1013, incomplete until the end of the war.
Yu 1014, incomplete until the end of the war.
''Yu 2001''-class
The Andō Iron Works-Tsukishima Factory build all of the Yu 2001-class boats. First boat was the second prototype of the Yu I type boats. They fitted a deck house root to the sail for improved crew comfort.
Yu 2001, launched on 12 February 1944, survived war.
