7. Sentoku Class

A submarine that’s an aircraft carrier seems like mating a fish and an elephant, but that didn’t stop several navies from trying. The Imperial Japanese Navy’s I-400 Sentoku Class boats of World War II were 6,500 tons, almost three times the size of U.S. Gato Class subs, and about the same displacement as a U.S. George Washington-class nuclear-powered missile sub from the early 1960s. The three Sentoku boats each carried three torpedo-equipped M6A Seiran floatplanes that would be launched by catapult, and then ditch in the water upon their return.