Not many people today are aware that the Soviet Union copied the US B-29 Superfortress after World War II to produce its first strategic bomber, the Tupolev Tu-4. It was based on three B-29's that landed in far eastern Russia after raids on Japan in 1944-45, and were interned there (their crews being returned to the USA).
The story of how the Russians copied the plane is explained in detail in Air & Space magazine. Here are a couple of excerpts.
Stalin had made three overtures to the United States under the Lend-Lease Act, a U.S. program launched in 1941 to provide materiel to friendly nations, to get B-29s as part of a general initiative to obtain heavy bombers. Washington rejected all requests for the heavies, but was generous with medium bombers, fighters, and transports. The Soviets even attempted a ruse in 1943, adding the B-29 to a long list of aircraft it wanted, but amused Lend-Lease officials denied the request.
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Stalin demanded that his new bomber be an exact copy of the B-29 because he wisely understood that even one concession would lead to a cascade of modifications, and any request to depart from this discipline would slow the process. Eager to maintain formal compliance with Stalin’s order, Tupolev chose not to take the mandate literally despite the presence of the secret police and the possibility of denunciation, reasoning that Stalin’s order pointed more toward ends than means. Thoughout the first year of the Tu-4 program, Tupolev walked a tightrope between Stalin’s requirements and practical concessions.
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The documentation required for the new bomber had been enormous. Retro-engineering dictated the analysis and photographing of some 105,000 parts. Tupolev’s team generated 40,000 detailed drawings, completed by a force of a thousand draftsmen. Exacting quality standards and the threat of police sanctions made the whole enterprise an exhausting experience. During the most critical phases of the program, workers were sometimes allowed only one day off each month. Any deviation raised the fear that someone, for personal benefit or revenge, might complain to the police.
One immense challenge was the difference between English measurements used by U.S. manufacturers and the metric system, which the Soviets used. Early on, Tupolev decided not to convert the U.S. units to the metric system, which would have been time consuming. The manufacture of aluminum panels exemplified the problem. The standard thickness of the aluminum skin on the B-29 was 1/16 of an inch (1.5875 millimeters). It was impossible for Soviet plants to fabricate metal sheets to that dimension. Tupolev opted to vary the thickness of the Tu-4’s skin between .8 and 1.8 millimeters, which actually had the effect of strengthening the aircraft’s structure in some areas. Despite such changes, the weight of the Tu-4 would turn out to be only one percent greater than the B-29. No less critical were other compromises made on electrical wiring as well as hydraulic pressure and fuel consumption.
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The Tu-4 made its public debut on Aviation Day in August 1947, at Moscow’s Tushino airfield. Foreign observers, including the Western powers—particularly their military attaches—were all invited. Three Tu-4s, followed by a Tu-70 passenger version, flew by at 600 feet. At the controls of one of the Tu-4s was Air Marshal Golovanov. When the Western observers counted three bombers, they assumed the Soviets were flying the long-lost interned B-29s. But the appearance of the Tu-70 clearly indicated that the Soviets were flying freshly cloned B-29s. This carefully staged event became a headline story in Western newspapers, though few realized how narrow the margin had been to get these four airplanes airborne. The Tu-70 had been fitted with cannibalized parts from [an interned US B-29 bomber] to make it airworthy.
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Only once in the cold war years of the 1950s did the Soviets threaten to deploy the Tu-4 in combat, although the details are unclear. In the first hours of the Hungarian Revolution of 1956, at a time when party secretary Nikita Khrushchev and the Soviet military were debating the options to counter a revolt in Hungary, several Tu-4 bombers were ordered to drop conventional bombs on Budapest. Saner minds prevailed, and the flight was called back while en route to the Hungarian capital, leaving Soviet ground forces and tanks to resolve the problem. This aborted flight remains one of the more controversial episodes associated with the history of the Tu-4.
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The Tu-4 project became the pathway for the rapid modernization of the Soviet aviation industry and gave expression to Stalin’s larger purpose: providing for Soviet national security, even military parity with the West. In the Tu-4 program, Stalin demonstrated a certain truth about the Bolsheviks: Personal ruthlessness did not necessarily preclude shrewdness or a disciplined flair for survival. While his instincts were not always perfect, Stalin nevertheless possessed a remarkable strategic sense—including an eye for the right airplanes—that shaped all his policies.
Stalin reorganized Soviet aviation for the post-war environment, compelling it to adopt a range of new technologies, materials, and techniques of manufacture. Technological inferiority persisted, but the baseline for a more sophisticated aviation sector had been established.
There's much more at the link. Highly recommended reading for aviation buffs and those interested in the early days of the Cold War.
Here's some video footage of the Tu-4.