Updated: September 28, 2025

A flying submarine, submersible aircraft or aero sub is a combination of a seaplane and a submarine. It is supposed to be able both to fly and to travel under water. Taking-off from the surface of water is also intended. Since the requirements for designing a submarine are practically opposed to those of an airplane, the performance expected from such a construction is usually rather moderate.

As early as 1920, the British trade journal, "Flying", reported conversations between the First Sea Lord and other military leaders and one of the principal aircraft manufacturers concerning a flying submarine ( Or submersible seaplane ). The all-metal craft, its hypothetical design illustrated in the article, was to be a twin-propeller airplane with retractable wings and a hermetically sealed fuselage. There was, however, apparently no further development of the project.