In 1936 Boris Ushakov proposed a unique concept to the military academy in Leningrad. Initially the plan was accepted and he received permission to proceed with the design.
The design was supposed to be built as an all-metal construction and operate at 100 knots in the air and 3 knots under water. The engines were supposed to be sealed shut by metal plates while under water. The flying submarine was supposed to house six hermetically sealed chambers in its hull and wings: Three chambers to hermetically seal the three aircraft engines (AM-34; 1000 HP; while starting 1200 HP, using the turbo compressor), as well as the hermetically sealed pilot's chamber, a chamber for the accumulator and another one for the electric engine. All the other empty spaces of the aircraft were supposed to be filled with water while submerging. The time for preparation and actual submerging were projected at 1.5 minutes. The hull was to be constructed as a riveted duralumin cylinder, measuring 1.4 m across and 6 mm thick. The cockpit was supposed to be flooded while submerging, after the flying instruments were lowered into a waterproof shaft. The crew was supposed to enter the aft command centre and control the submarine from there.
The outer skin of the wings and the empennage was to be made of steel, the floats of duralumin. These parts were supposed to be filled with water while submerging, so they did not have to be designed for the water pressure in diving depth. The water was supposed to enter by itself through opened valves.
The containers for fuel and lubricant were to be placed in rubber reservoirs in the flying submarine's hull. As a corrosion prevention, the flying submarine was supposed to be treated with special paints and varnishes.
Two special mounts for 18 inch torpedoes were supposed to be placed under the hull. The payload was supposed to be 44.5% of the take-off mass. This is a typical value for heavy aircraft of the time. For surfacing, the excess water was supposed to be pumped out of the empty spaces. The electric engine was designed as an underwater drive.
The flying submarine was supposed to be used on the open sea for torpedo attacks on opposing ships. It was supposed to track these ships and await their arrival at the projected course while submerged. In case the opposing ship would not pass closely enough, another trial was supposed to be possible. Therefore the flying aircraft would have had to surface after the opposing ship was out of sight, track them again and await them again at the correct position.
Another projected use was entering naval areas and naval bases, which were blocked by mine belts. The flying submarine was supposed to pass the mines while in the air and then land inside an opposing restricted area, bay or naval base at night, submerge and act as a submarine. During the day, it would then have been able to gather intelligence on opposing forces, determine navigable water, or use an opportunity to attack. Especially the combined use of multiple flying submarines offered great opportunities. In theory, three flying submarines would have been able to form a 15 km long cordon sanitaire, able to block the projected way of opposing ships.
The project was expected to counter a disadvantage of submarines, their bad maneuverability. Expectations were especially high for the ability to repeat attack maneuvers 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 suspended and classified.
Convair Flying subplane
In 1962 the Convair company made a proposal to the US Navy for a Flying submarine. The purpose of this was identical with the Soviet proposal of the 1930's.
It dispensed with heavy floats, relying instead on its streamlined fuselage, like the hull of a flying boat, to land on the water. In a paper in the September 1964 issue of Naval Institute Proceedings (p 144), hydrodynamics engineer Eugene Handler at the US Bureau of Naval Weapons claimed this flying sub would be ideal for attacking Soviet shipping in the Baltic, Black and Caspian seas.
Convair drew up detailed designs and even built scale models which were tested in water tanks. Though the results looked promising, the project never made it any further; it was cancelled by Congress in 1966.
Both models Unicraft resin 1/72