In the USSR, a project for a flying submarine was proposed. From 1934 to 1938, the flying submarine project was led by Boris Ushakov. The flying submarine was a three-engine, twin-float seaplane equipped with a periscope. While studying at the F. E. Dzerzhinsky Higher Naval Engineering Institute in Leningrad (now the Naval Engineering Institute), from 1934 until his graduation in 1937, student Boris Ushakov worked on this project, which combined the capabilities of a seaplane with those of a submarine. The core of the invention was a seaplane capable of submerging underwater. The project was suspended in 1939 and resumed only in 1943. Ultimately, a prototype was built in 1947, but by that time, the Soviet naval doctrine had changed, and the project was discontinued.