Japanese Submarine I-402

Imperial Japanese Navy submarine I-402, was one of three completed Sen Toku I-400 class submarine aircraft carriers, which proved to be the largest prior to nuclear submarine development. Each were able to carry three Aichi M6A Seiran floatplanes. In 1942 18 of these vessels were planned, however after increased shipping losses and the rising scarcity of alloys, only five were expected to be built. By 1944 only three had been completed (I-400 at Kure, I-401 and I-402 at Sasebo). Although I-402 never saw combat it was intended for attacks on the eastern seaboard of the United States and the eastern locks of the Panama Canal.

Characteristics
I-402 was powered by four 3,000 horsepower diesel engines. The massive I-400 class submarine displaced 6,500 tons and had an overall length of 380 feet compared to the most numerous IJN submarine type, the B1 which only displaced 2,584 tons and had a length of 356 feet. The most notable characteristic of the I-402 was its ability to carry three Aichi M6A Seiran seaplane dive bombers. I-402 had a figure-eight hull shape for additional strength to handle the on-deck hangar for housing the three aircraft. The wings of the Seiran folded back, the horizontal stabilizers folded down, and the top of the vertical stabilizer folded over so the overall forward profile of the aircraft was within the diameter of its propeller. The planes were launched from a 120-foot catapult on the deck of the giant submarine. In addition, it had four anti-aircraft guns and a 14 cm 40 caliber deck gun as well as a suitable complement of twenty Type 95 torpedos for commerce raids.

Post War Inspections
I-402 along with her sister ships were captured by the United States Navy after the war. They were taken to Sasebo Bay for evaluation. While there, the Soviet Union planned to send inspectors to also study the unknown vessels. To keep the technology out of the hands of the Soviets, Operation Road's End was instituted. I-402 along with twenty other submarines were filled with C-2 explosive charges and scuttled off the Gotō Islands.