We often hear about Nazi super-weapons — there was a whole cable channel dedicated to Hitler, wasn’t there? — but the Japanese had submarine aircraft carriers by the end of the war:
The I-400 subs were the largest ever built until the Ethan Allen-class of nuclear subs in 1961. The I-400 subs not only could travel one and a half times around the world without refueling, they carried three Aichi M6A1 attack planes, which they launched off their bow when surfaced, effectively making them underwater aircraft carriers.
Soon after the war, the US Navy sank the captured super-subs, to test its new top-secret “robot” torpedo — but really to keep them out of our supposed Allies’ hands:
The Hawaii Undersea Research Laboratory, or HURL, has found the rusting hulks off the coast of Oahu.
Now all they need is a little clean-up and a Wave Motion Engine…
“The I-400 was put into dry dock at Pearl Harbor in February 1946, so U.S. Naval intelligence could conduct a thorough investigation of their technology. When the Russians asked to examine the subs, the U.S. Navy sailed them off the coast of Oahu where they were torpedoed and sunk. The Russians filed a protest but it was too late. The Cold War was already underway.”
The Japanese had a dozen submarine aircraft carriers since the war’s start. That model had one floatplane only.
They were the nation most invested in floatplanes. They built four floatplane cruisers, with 20 floatplanes, and several floatplane tenders. Their main fleet recon was in the hands of two recon cruisers, Chikuma and Tone, each with about 6 floatplanes.