The I-400-class submarine, also called the Sen Toku class, was a class of large Japanese Imperial Navy submarines developed during World War II. They were planned to be used as aircraft carriers, but only three were completed before the end of the war. The I-400-class submarines were the largest submarines ever built, with a length of 122 metres (400 ft) and a displacement of 5,227 tonnes (5,156 long tons). They were powered by two diesel engines and two electric motors, giving them a top speed of 23 knots (43 km/h; 26 mph) on the surface and 10 knots (19 km/h; 12 mph) submerged. They could carry a crew of 144 men. The I-400-class submarines were equipped with a hangar and catapult for two Aichi M6A Seiran seaplanes. The seaplanes could be launched and recovered at sea, giving the submarines the ability to launch air strikes against enemy targets. The I-400-class submarines were designed to operate in the Pacific Ocean, and they were equipped with a number of features to make them suitable for long-range operations. They had a range of 36,000 nautical miles (67,000 km; 41,000 mi) on the surface and 18,000 nautical miles (33,000 km; 21,000 mi) submerged. They also had a number of watertight compartments to protect them from damage. The I-400-class submarines were a revolutionary design, and they were far ahead of their time. However, they were too late to have a significant impact on the war. Only three were completed, and they were never used in combat. The I-400-class submarines were sunk after the war. One was sunk by American forces in 1946, and the other two were sunk by the Japanese themselves in 1948.
