The I-400 was a class of submarines used by the Imperial Japanese Navy during World War II. It was notable for being one of the largest submarines of its time, designed to carry and launch aircraft. Each I-400 could carry up to three Aichi M6A Seiran floatplanes, which could be deployed for reconnaissance or bombing missions. These submarines were equipped with advanced technology for their era, including a unique hangar and catapult system for launching aircraft while submerged. The I-400 class played a strategic role in Japan's naval operations, but only a few were completed before the war ended, limiting their impact on the conflict.