Submarine aircraft carriers were developed by the Imperial Japanese Navy to a greater extent than any other navy, before and during World War II. In total, 42 were built, as listed below (other sources say 47). Although other navies had experimented with submarine aircraft carriers, by World War II the IJN was the only navy (aside from one fielded by the French Navy) using them. They had little effect on the war, although two were used to carry out attacks on the continental United States.
They almost all carried a single floatplane for reconnaissance only, being either the Watanabe E9W, Yokosuka E6Y, or Yokosuka E14Y. The only exceptions being the Junsen Type A Mod.2 and Type Sentoku, who carried respectively two or three Aichi M6A Seiran bomber. All apart from the first (I-5) had a fixed catapult and hangar or hangars, generally on the forward deck.