Combat aviation of the USSR: long-range bomber Il-4 (DB-3F). All-metal twin-engined monoplane with closed cockpit and retractable landing gear. The first flight – 1936.

Museum of the Great Patriotic War, Moscow

The Ilyushin Il-4 (DB-3F) was a Soviet twin-engined long-range bomber and torpedo bomber, widely used by the Soviet Air Force and Soviet Naval Aviation during World War II.

In 1938, the Ilyushin design bureau redesigned the Ilyushin DB-3 to ease production and improve its performance, the revised version receiving the designation DB-3F (Forsirovanniye or “boosted”). The aircraft’s internal structure, particularly the wings, was extensively changed, eliminating the need for hand finishing of the structure, and with duralumin replacing the large scale use of steel in the earlier version.

The aircraft’s fuel system was redesigned, increasing its internal capacity while reducing the number of fuel tanks. The fuselage nose was lengthened to give more room for the navigator/bombardier while reducing drag. The prototype DB-3F, powered by the same 949 hp (708 kW) Tumansky M-87B engines of the DB-3M, was piloted on its maiden flight by Vladimir Kokkinaki on 21 May 1939.

It successfully passed through state acceptance tests and entered production in January 1940, with the 1,100 hp (820 kW) Tumansky M-88 quickly replacing the M-87.

The DB-3F was redesignated Il-4 in March 1942. Some series had wooden outer wings and front fuselages to conserve metals, and throughout the production, engines and fuel tanks were upgraded for improved performance while retaining the same range. However the most notable change was the addition of larger defensive guns in the turret, using the 12.7 mm (0.5 in) UBT machine gun in place of the earlier 7.62 mm (0.3 in) weapons. In addition, it was found that the gunners were attacked first, so blocks of armor were placed around the gunner positions.

This extra weight was not offset by the newer engines however, and the Il-4 proved to be slower than the earlier versions at only 404 km/h (251 mph). An attempt to improve performance was made as the Il-6, adding large diesel engines and heavier armament. The engines proved unreliable and production was never started. The Il-4 remained in production until 1945, when just over 5,200 had been built.

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