The Tupolev Tu-4 was for all intents and purposes a Boeing B-29 Superfortress Intercontinental Bomber.
When they came into service on their first mission on June 5th, 1944, they were the baddest things to hit the skies. They were bigger, faster, could fly higher, longer and carry a heavier payload. To quote the History Channel, they were "Buck Rogers" at the time. The Russians saw this and wanted it for themselves, but more on that later.
They still, however, needed a place to land if and when they were damaged after a bombing run over Japan. The Russians had a peace, however fragile, with the Japanese. The peace with the western Allied forces was uneasy as well. They played nice until Hitler was gone. Understandably, he could not let these bombers that were burning down Japanese cities land in Siberia. Stalin did not want, and probably would have lost a 2 front war.
Well, bombs are falling and flak is being shot up over Japan. Lo and behold, 3 B-29's end up in Russia. Stalin kept the planes, but arranged "escapes" for the crews, to appease the Americans and Japanese. Stalin then ordered an exact replica of these aircraft that Americans spent $3 billion to develop.
The Tu-4 is almost a rivet by rivet copy of the B-29, with a few exceptions. The Russians were unable to replicate some of the more complex systems of the B-29 Superfortress. They had a tough time with the remote controlled guns among other things. They also had problems with the thickness of the aluminum skin, as the Russians used the metric system and the Americans used the imperial system. Also, some parts were just plain purchased in post war surplus sales or stolen.
This aircraft was introduced to the west during a parade that they attended with Stalin, during which 3 of them flew over head. The Americans thought these were just the 3 they landed there, until a 4th flew over head. The last one was actually a Tu-70, a passenger version.
This was just the beginning of a long and scary arms race, and brought new tensions to a very young Cold War.