I-400 (伊号第四百潜水艦, I-gō-dai yon-hyaku-sensuikan) was an Imperial Japanese Navy Sentoku-type (or I-400-class) submarine commissioned in 1944 for service in World War II. Capable of carrying three two-seat Aichi M6A1 "Seiran" (Mountain Haze) float-equipped torpedo bombers, the Sentoku-class submarines were built to launch a surprise air strike against the Panama Canal. Until 1965, the Sentaku-type submarines—I-400 and her sister ships I-401 and I-402 —were the largest submarines ever commissioned.
