The Soviet Union tried to develop a flying submarine during World War II, whose production never exceeded design phase. At the Naval Engineering Institute, a flying submarine project was headed by engineer Boris Ushakov.
During his studies at the Dzerzhinsky naval engineers' academy in Saint Petersburg, which he finished in 1937, Boris Ushakov presented a draft for a project, which could unite the capabilities of an aircraft with those of a submarine. To be precise, this draft showed a seaplane able to dive.
In the following years, the project was revised and presented in multiple variations, enabling him to test the capacity and durability of particular components. In April 1936 the reviewer determined that Ushakov's was interesting and to be implemented. In July 1936 the draft project “Flying submarine” was checked and evaluated positively by the scientific research committee of the forces. The committee recommended to continue the project, to test its realisability using calculations and lab tests.
In 1937 the project was included into plan “W” (russ. “В”) of the committee. However, the project was cancelled after a reevaluation. Ushakov, by the time a “military technician 1st class” in department “W” of the committee continued the project in his spare time.
In 1938 the draft and the fundamental tactical-technical elements of Ushakov's flying submarine were evaluated once more by the 2nd department of the committee.
The project was expected to counter a disadvantage of submarines, their bad manoeuvrability. Expectations were especially high for the ability to repeat attack manoeuvres using a short flight to a different attack location, if opposing ships would not pass closely enough. This was seen as one of the flying submarine’s main advantages.
In 1939 the project was temporarily suspended and classified. In 1943, on the orders of NKVD chief Lavrentiy Beria, the project was resumed. In 1947 the first test of the flying submarine was performed. In 1953, the project was closed by order of Communist Party First Secretary Nikita Khrushchev. The design never "got off the ground".