Submarine aircraft carrier I-400
The Sen Toku I-400-class submarines of the Imperial Japanese Navy were the largest submarines of World War II, and remained the largest ever built prior to the development of nuclear ballistic missile submarines in the 1960s.
They were able to carry three Aichi M6A Seiran aircraft, each carrying an 800 kilogram bomb 650 miles, at 295 miles per hour. A crew of four could prepare and get all three airborne in 45 minutes. The planes were launched from a 120-foot catapult on the deck. The existence of the Seiran was unknown to Allied intelligence.
Admiral Yamamoto planned to use the sen toku (secret submarine attack) in 1945 to attack the Panama Canal. The bombing flights would have been one-way trips. None of the pilots expected to survive the attack, a tactic called tokko. Each pilot was presented with a tokko short sword, symbolic of the ultimate sacrifice.
This never materialised. Japan surrendered, and on August 22, 1945, the crews of the submarines were ordered to destroy all their weapons. The torpedoes were fired without arming and the aircraft were launched without unfolding the wings and stabilizers. When I-401 surrendered to an American destroyer, the U.S. crew was astounded at its size. The commander of the submarine fleet, Captain Ariizumi, apparently decided on suicide rather than surrender to the Americans. He requested that his body be wrapped in the Japanese flag and buried at sea, and shot himself. His body was never presented as proof of his death.