Nice shots!

In 1944 three B-29s made emergency landings in the Soviet Union after receiving damage during bombing raids in Japan and Manchuria. The Soviets had demanded B-29s as part of the 'lend-lease' agreement, but the US refused to provide them with such an advanced aircraft. When Stalin got his hands on these aircraft he kept them (ignoring American demands for the aircraft to be either 1-destroyed, or 2-returned to the US). All three of the aircraft were flown to the Tupolev headquarters in Moscow.

Prior to the acquisition of these three aircraft Stalin had ordered the development of a heavy bomber, similar to the B-29. As soon as the Soviets acquired these US bombers the Soviet heavy bomber program was cancelled, and Tupolev began to build aircraft almost identical to the B-29, the Tu-4.

Mike JG is right also. Because the B-29 was so well built and the measurements needed to be so precise, the Soviets had to invest in more modern equipment simply to build the aircraft. Needless to say, this was very expensive. However, the Soviets got their heavy bomber, although when it entered service in 1949 it was already obsolete as it was deemed inadequate against the US all-weather interceptors (it was actually inferior to the B-29 due to poor build quality too).

It may be hard to see, but without the three B-29s the Soviets acquired in 1944, aircraft such as the Tu-95 may never have taken off.