The I-400-class submarine (I-yon-hyaku-gata sensuikan?) Imperial Japanese Navy submarines were the largest submarines of World War II and remained the largest ever built until the construction of nuclear ballistic missile submarines in the 1960s. The IJN called this type of submarine Sentoku type submarine (Sen-Toku-gata sensuikan, Submarine Special?). The type name, was shortened to Toku-gata Sensuikan (Special Type Submarine?). They were submarine aircraft carriers able to carry three Aichi M6A Seiran aircraft underwater to their destinations. They were designed to surface, launch their planes, then quickly dive again before they were discovered. They also carried torpedoes for close-range combat (Source Wikipedia)