Ilyushin Il-4

The Il-4 started life as a quickly produced bomber prototype called the TsKB-26. Parts of the fuselage and cockpit were taken from the TsKB-12 (Polikarpov I-16) fighter, married to new wings made of welded steel U-beams and tubes. Only a few were built before attention turned to the updated TsKB-30, which included a new fuselage using the same construction methods. Welding the beams required three welds per joint, so the plane took a huge amount of time to build. Nevertheless the design had excellent range and was quite sturdy. It was put into production in 1936 as the DB-3, 1,528 being completed by 1939.

This was followed by the updated DB-3M, which looked similar with the exception of a much larger and more rounded nose. However the plane was actually quite different internally. Using lessons learned from the Li-2 (Douglas DC-3) the entire plane was re-built using T shaped formers instead of the tubes and U-beams. This lead to a tremendous reduction in the time needed to build the plane, and the DB-3M was hurriedly put into production.

A change of engine from the 950hp M-87B to the 1,100hp M-88 resulted in the DB-3F, which were eventually renamed in 1942 as the Il-4. Some series had wooden outer wings and front fuselage to conserve metals, and throughout the production engines and fuel tanks were upgraded for more performance while keeping the same range. However the most notable change was the addition of larger defensive guns in the turret, using the 12.7mm (50cal) UBT in place of the earler 7.62's. In addition it was found that the gunners were attacked first, so blocks of armor were placed around the gunner positions.

All this extra weight wasn't offset by the newer engines however, and the Il-4 proved to be slower than the earlier versions at only 404km/h. An attempt to improve performance was made as the Il-6, adding large diesel engines and heavier armament. The engine proved unreliable and production was never started. The Il-4 remained in production until 1944, when just over 5,200 had been built.

Although the Il-4 was only a medium, it had the range to be used on strategic missions. The VVS wasn't terribly interested in this role, but nevertheless the Il-4 was used on several highly publicised raids against Berlin. Most would be used on much shorter range missions, often adding another 1,000kg of bombs under the wings, in addition to the internal 2,500kg.