Ilyushin’s DB-3/Il-4 medium bomber entered service in 1937 and served throughout World War II as a standard bomber and torpedo-bomber for both the air force and the navy. A few bombed Helsinki during the Winter War against Finland. Three hours after Soviet forces had crossed the border and started the Winter War, aerial bombardment of Helsinki began. The most intensive bomb raids were during the first few days.
Helsinki was bombed a total of eight times during the Winter War. Some 350 bombs fell on the city, resulting in the death of 97 people and the wounding of 260. In all, 55 buildings were destroyed. Finland lost only 5 percent of its total man-hour production time due to Soviet bombings. Nevertheless, bombings effected thousands of civilians as the Soviets launched 2,075 bombing attacks on 516 localities. Air raids killed 957 Finnish civilians. The city of Viipuri, a major Soviet objective, was almost leveled by nearly 12,000 bombs.
In 1938 a version of the DB-3 was developed with a totally new, easily-built airframe and equipped with two 765 hp (570 kW) M-85 engines but these were soon replaced with two 960 hp (716 kW) M86 engines. As a result the appearance of the design was completely changed, the nose being slim, streamlined and with a large glazed area, with the nose turret of the DB-3 (DB for Dalni Bombardirovschik or long range bomber) replaced by a swivel gun mounting. State acceptance trials were completed successfully in June 1939 and by the end of that year the type was readied for quantity production. This new version was known as the lIyushin DB-3F, later redesignated Il-4 when delivered in quantity to the bomber regiments of the long-range air arm, the ADD. A small number had the same type of dorsal turret as the DB-3, but this was soon replaced by a more effective design. Additionally, the ventral machine-gun ring was replaced by a more complex semi-retractable mount.
The Il-4 remained in large scale production until 1944, the number built being 5,256. The original M-87A engine was replaced by the more powerful M-88B with a two-speed supercharger in 1942. Most aircraft built in 1942 were completed with wooden wing spars as a result of shortage of light alloys due to the German invasion, but metal components were reintroduced in late production machines when new plants in Siberia became operational.
In addition to its use for long-range bombing raids, the Il-4s of the ADD's various long-range bomber corps were used frequently in attacks on tactical targets immediately behind enemy lines, carrying their maximum bombload. The Il-4 also came to be used widely by the mine/torpedo bomber regiments attached to the Baltic, Black Sea and Northern Fleets. When deployed in a torpedo-carrying role the Il-4 was armed with a 2,072 lbs (940 kg) 45-36-AN (Iow-level) or 45-36-AV (high-Ievel) torpedo. There was also provision for an auxiliary external fuel tank mounted under the rear fuselage. During 1943 the Ilyushin Il-4 also saw duties in the reconnaissance role and some even were converted to glider tugs.
The Il-4 was a robust and successful aircraft, a number surviving into the post-war period for use in a variety of support roles. It had sufficient longevity to earn the NATO codename 'Bob'. Four Il-4s purchased from German war booty stores were used by the Finns against the Soviet forces from 1943 to 1945.