The Sen Toku I-400-class 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. They were submarine aircraft carriers able to carry three Aichi M6A Seiran aircraft underwater to their destinations. They were designed to surface, launch the planes then dive again quickly before they were discovered. They also carried torpedoes for close-range combat. The I-400-class was designed with the range to travel anywhere in the world and return. A fleet of 18 boats was planned in 1942, of which only three were completed.
Located approximately amidships on the top deck was a cylindrical watertight aircraft hangar, 31 m (102 ft) long and 3.5 m (11 ft) in diameter. The outer access door could be opened hydraulically from within or manually from the outside by turning a large hand-wheel connected to a rack and spur gear. The door was made waterproof with a 51-millimeter-thick (2 in.) rubber gasket.
The Daily Omnivore 
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