The Sincerest Form

The Soviet Tupolev Tu-4 strategic bomber of the 1950s was a reverse-engineered copy of the American Boeing B-29 Superfortress. Stalin wanted a strategic bomber, so when three B-29s were forced to land in Soviet territory in 1944, he ordered clones made, and 20 were ready by 1947, despite the engineering challenges caused by non-metric American specifications.

The Soviets revealed their coup during a Moscow parade in August 1947. When three aircraft flew overhead, Western analysts assumed they were the three captured B-29s. Then a fourth appeared.

(Thanks, Kevin.)