Ushakov Flying Submarine
One of those designs that if it wasn't real it would not be believable.
Soviet design for a flying submarine, travelling 100kts airborne and only 3 knots submerged, while carrying 2 torpedoes.
Initially submitted in 1936, the project was cancelled in 1937. Redrafted in 1938, it was again suspended in 1939. In 1943 the project was again resumed, before finally being closed in 1953.