The I-400 class submarine was the brainchild of Admiral Isoroku Yamamoto, Commander-in-Chief of the Japanese Combined Fleet. Shortly after the attack on Pearl Harbor in December 1941, he conceived the idea of taking the war to the United States mainland by making aerial attacks against cities along the US western and eastern seaboards using submarine-launched naval aircraft. He commissioned Captain Kameto Kuroshima to make a feasibility study.
Yamamoto submitted the resulting proposal to Fleet Headquarters on 13 January 1942. It called for a fleet of 18 large submarines capable of making three round-trips to the west coast of the United States without refueling or one round-trip to any point on the globe. They had also to be able to store and launch at least two attack aircraft armed with one torpedo or 800 kg (1,800 lb) bomb. By 17 March general design plans for the submarines were finalized. Construction of I-400 commenced at Kure Dock Yards on 18 January 1943, and four more boats followed: I-401 (April 1943) and I-402 (Oct 1943) at Sasebo; I-403 (Sept 1943) at Kobe and I-404 (February 1944) at Kure. Only three were completed.
Following Yamamoto's death during an inspection tour of the Solomon Islands in April 1943, the number of aircraft-carrying submarines to be built was reduced from eighteen to nine, then five and finally three. Only I-400 and I-401 actually entered service; I-402 was completed on 24 July 1945, three weeks before the end of the war, but never made it to sea.