I-402 was a Japanese submarine during World War II, notable for being one of the largest submarines ever built. Launched in 1943, it was designed to carry and launch Kō-hyōteki (special attack) aircraft, specifically the Kaiten torpedoes, which were manned torpedoes used for suicide attacks against enemy ships. The submarine was part of the Imperial Japanese Navy and had a unique design that allowed it to operate both underwater and on the surface. I-402 was ultimately scuttled in 1946 after the war, and its remains were discovered in the 1990s, providing insights into submarine technology of that era.