In the final two years of World War II, the Imperial Japanese Army constructed transport submarines — officially the Type 3 submergence transport vehicle and known to the Japanese Army as the Maru Yu — with which to supply its isolated island garrisons in the Pacific.

The Yu I type was produced in four subclasses, each produced by a different manufacturer and differing primarily in the design of their conning towers and details of their gun armament, although one source[1] states that the Yu 1001 subclass differed from the original Yu 1 sublcass in other ways, being longer, having a slightly larger displacement and more powerful diesel engine that increased the maximum speed by 2 knots (3.7 km/h; 2.3 mph), and probably having no deck gun installed.

[citation needed] Yu 1001 spent her operational career in Japanese home waters.

[citation needed] In January 1945, several Type I transport submarines were sent to operate from Shimoda on the southern tip of the Izu Peninsula in Shizuoka Prefecture on Honshu,[1] and the submarines began transport missions from Shimoda in March 1945.

[1] It is not clear when Yu 7 began operations from Shimoda, but she made a round-trip supply voyage from Shimoda to Hachijō-jima in the Philippine Sea sometime during 1945 as well as a round-trip supply voyage from the Army Transport Submarine Base on the Seto Inland Sea at Mishima in Ehime Prefecture[4] on Shikoku to Ōshima Island in March 1945.