It has often been said that World War II was won with British intelligence, American steel, and Russian blood. The Soviet Union was crucial in defeating Hitler's military, but that didn't mean they were friends with the US. The Americans sent Stalin tons of weapons, military hardware, and food, but one thing the US did not want to share was the Boeing B-29 Superfortress, the most advanced aircraft of the time, and the ultimate war machine.
Luckily for Stalin, B-29 crews were instructed to land in Russia in case of emergencies, and in the summer of 1944, exactly such an emergency befell three B-29s during a bombing raid to Japan. The three aircrafts—General H.H. Arnold Special, Ding How, and Ramp Tramp—landed in Vladivostok, and at once, the Soviet whisked them away to a facility in Moscow. The crews were sent back home, but not after desperate pleas from the US. Demands for the return of the planes were ignored.
With these three aircrafts, Soviet engineers began one of the most complex and audacious reverse-engineering projects ever. Of the three, one was dismantled. To keep track of the growing mountain of parts, the second one was use as reference. The third was used for test flight.