Toward the end of
World War II, the Soviet Union saw the need for a strategic bombing capability similar to that of the Western Allies. The Soviet VVS air arm had the locally designed
Petlyakov Pe-8 four-engined "heavy" in service at the start of the war, but besides suffering complicated engines 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
Tupolev OKB. 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 twenty 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
U.S. customary measurements was 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. Despite those challenges, the prototype Tu-4 weighed only 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 superior to that found on the B-29s. 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. 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 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 would enter large-scale service by 1949. The aircraft was first displayed during a flyover on 3 August 1947 at the
Tushino Aviation Day parade. At first three aircraft flew over and the Western observers assumed that they were merely the three B-29 bombers which they knew had been diverted to the Soviet Union during World War II. Minutes later a fourth aircraft appeared, and the observers realized the Soviets had reverse-engineered the B-29. Entry into service of the Tu-4 threw the
U.S. Air Force into panic since the aircraft 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. ==Operational history==