In the mid-20th century, several countries had plans to construct a flying submarine.
The Black Sea carries strategic importance the many countries that share its shores: Ukraine, Russia, Turkey, Romania, Georgia, and Bulgaria. During the Cold War, the Black Sea was pretty much dominated by the Soviet Union. The chances of the United States (or anyone else) sneaking a submarine into these waters was slim to nil. The same went for the Caspian Sea and the Baltic.
The United States Navy wanted to find a way to get some submarine support into these strategic seas. In the early 1960s they commissioned an exploration into a new kind of vehicle: a submersible seaplane, or a flying submarine.
I know this sounds like a piece of James-Bond-level nonsense, but the logic wasn’t terrible. A plane could fly above the water and spot an enemy ship or submarine, and then that plane could dive underneath that water to attack it. A little like a gannet, I guess, plunging into the water to catch fish. And it would also be a great way to get submarines into challenging bodies of water like the Black Sea.
That navy project – the Convair Submersible Seaplane – never got further than the drawing board. Both the Soviet Union and Britain also explored the flying submarine concept, but once again their plans never got off the ground (or off the water).
Just one attempt, the Reid Flying Submarine 1, actually got to the prototype stage. Cobbled together from spare parts by an enthusiastic American defence contractor, the RFS-1 could both fly and dive… but neither particularly well. In its 1964 demonstration it flew 10 metres above the surface and dove 2 metres below it. The best thing about this vessel was its open cockpit. Yup, the pilot was not sealed off from the water: whenever it dove they had to put on a scuba set.