Single-engine, low-wing monoplane fighter, developed by the American aircraft manufacturer Bell Aircraft Corporation in the second half of the 1930s. It was the first fighter in the world to have a tricycle landing gear and the first to have the engine installed in the center of the fuselage, behind the pilot. The Bell P-39 Airacobra is still one of the most controversial fighter aircraft of World War II. With its sleek racing lines, apparent high speed and powerful gun, it received much positive publicity before the United States entered the war, but was rejected as a front-line fighter by the RAF and was generally unpopular among American pilots who flew it in combat. Rejected by the RAF after only one combat mission, it was on the other hand particularly appreciated by the Soviet Union Air Force, which received almost half of the production, thanks to the Lend-Lease Act, and used it, mainly at low altitude, in the roles of free fighter and interceptor of enemy bombers and fighter-bombers. From the Bell workshops, located in Buffalo, came out about 9,600 examples of P-39 Airacobra, divided into ten versions, in a period of time ranging from 1938 to 1944. The engine unit of the Bell P-39 was, throughout its evolutionary process, the Allison V-1710, a twelve-cylinder with V architecture and liquid cooling with powers from 1,150 hp to 1,325 hp.