Submarines of the Imperial Japanese Navy
The submarines ("I-52"-class) were submarines of the Imperial Japanese Navy, designed and built by Mitsubishi Corporation, between 1943 and 1944, as cargo carriers. They were quite long and carried a crew of up to 94 officers and enlisted. They also had a long cruising range at a speed of .
Aichi M6A
From the late 1920s, the Imperial Japanese Navy had developed a doctrine of operating floatplanes from submarines to search for targets.
In December 1941, Commander-in-Chief of the Japanese Combined Fleet, Admiral Isoroku Yamamoto, proposed constructing a large fleet of submarine aircraft carriers (also designated STo or "sen-toku" — special submarine) whose purpose was to mount aerial attacks against American coastal cities. The submarines would surface to launch their aircraft by catapult, submerge to avoid detection, then surface again to retrieve the aircrews who would ditch their planes nearby. By June 1942, the plan was to build a fleet of eighteen such subs. This was later cut to nine, then five and finally just three as Japan's wartime fortunes declined.