The Tupolev Tu-4 (Russian: Туполев Ту-4; NATO reporting name: Bull) is a piston-engined Sovietstrategic bomber that served the Soviet Air Force from the late 1940s to mid-1960s. It was reverse-engineered from the American Boeing B-29 Superfortress.
Toward the end of World War II, the Soviet Union saw the need for a strategic bombing capability similar to that of the United States Army Air Forces. The Soviet VVS air arm had the locally designed Petlyakov Pe-8 four-engined “heavy” in service at the start of the war, but only 93 had been built by the end of the war and the type had become obsolete. The U.S. regularly conducted bombing raids on Japan, from distant Pacific forward bases using B-29 Superfortresses. Joseph Stalin ordered the development of a comparable bomber.
The U.S. twice refused to supply the Soviet Union with B-29s under Lend Lease. However, on four occasions during 1944, individual B-29s made emergency landings in Soviet territory and one crashed after the crew bailed out. In accordance with the Soviet–Japanese Neutrality Pact, the Soviets were neutral in the Pacific War and so the bombers were interned and kept by the Soviets. Despite Soviet neutrality, the U.S. demanded the return of the bombers, but were refused. Three repairable B-29s were flown to Moscow and delivered to the TupolevOKB. One B-29 was dismantled, the second was used for flight tests and training, and the third was left as a standard for cross-reference. The aircraft included one Boeing-Wichita −5-BW, two Boeing-Wichita −15-BWs and the wreckage of one Boeing-Renton −1-BN, comprising three different models from two different production lines, at Wichita and Renton. Only one of the four had deicing boots, as would be used on the Tu-4. The fourth B-29 was returned to the US along with its crew with the end of the Soviet-Japanese peace. The Soviets declared war on Japan two days after the atomic bombing of Hiroshima, in accordance with the Yalta Agreement.
Stalin told Tupolev to duplicate the Superfortress in as short a time as possible instead of continuing with his own comparable ANT-64/Tu-10. The reverse-engineering effort involved 900 factories and research institutes, which finished the design work during the first year, and 105,000 drawings were made. By the end of the second year, the Soviet industry was to produce 20 copies of the aircraft, ready for state acceptance trials.
The Soviet Union used the metric system and so sheet aluminium in thicknesses matching the B-29’s imperial measurements were unavailable. The corresponding metric-gauge metal was of different thicknesses. Alloys and other materials new to the Soviet Union had to be brought into production. Extensive re-engineering had to take place to compensate for the differences, and Soviet official strength margins had to be decreased to avoid further redesign. However despite those challenges, the prototype Tu-4 weighed only 340 kg (750 lb) more than the B-29, a difference of less than 1%.
The engineers and suppliers of components were under pressure from Tupolev, Stalin, and the government to create an exact clone of the original B-29 to facilitate production. Tupolev had to overcome substantial resistance to use equipment that was not only already in production but also sometimes better than the American version. Each alteration and every component made was scrutinized and was subject to a lengthy bureaucratic decision process. Kerber, then Tupolev’s deputy, recalled in his memoirs that engineers needed authorization from a high-ranking general to use Soviet-made parachutes. Differences were limited to the engines, the defensive weapons, the radio (a later model used in lend-lease B-25s was used in place of the radio in the interned B-29s) and the identification friend or foe (IFF) system since the American IFF was unsuitable. The Soviet Shvetsov ASh-73 engine was a development of the Wright R-1820 but was not otherwise related to the B-29’s Wright R-3350 The ASh-73 also powered some of Aeroflot‘s remaining obsolescent Petlyakov Pe-8 airframes, a much-earlier Soviet four-engined heavy bomber, whose production was curtailed by higher-priority programs. The B-29’s remote-controlled gun turrets were redesigned to accommodate the Soviet Nudelman NS-23, a harder hitting and longer ranged 23 mm (0.91 in) cannon. Additional changes were made as a result of problems encountered during testing related to engine and propeller failures, and equipment changes were made throughout the aircraft’s service life.
The Tu-4 first flew on 19 May 1947 and was flown by test pilot Nikolai Rybko. Serial production started immediately, and the type entered large-scale service in 1949. Entry into service of the Tu-4 threw the USAF into a panic since the Tu-4 possessed sufficient range to attack Chicago or Los Angeles on a one-way mission, and that may have informed the maneuvers and air combat practice conducted by US and British air forces in 1948 involving fleets of B-29s. The tests were conducted by the RAF Central Fighter Establishment and co-operative US B-29 groups and involved demonstration of recommended methods of attack against B-29/Tu 4-type bombers using RAF Gloster Meteor and de Havilland Vampire jet fighters. The Soviets developed four different midair refueling systems to extend the bomber’s range, but these were fitted to only a few aircraft, and only a small number of the final design were installed on operational aircraft before the Tu-4 was superseded by the Tu-16.