The B-29 Boeing Model 345 was one of the biggest aircraft to serve during World War II. It was one of the most advanced bombers of its time. It was the most used aircraft in the U.S. bombing against Japan in the final months of World War II, and B-29s carried the atomic bombs that destroyed Hiroshima and Nagasaki. The B-29 stayed in service for a long time after the war ended. By the time it was retired in the 1960s, some 3,900 planes had been built.