The Boeing B-29 Superfortress’s original internal designation was Model 345.
Boeing developed the Model 345 in response to a United States Army Air Corps requirement for a long-range, high-altitude heavy bomber. The design incorporated pressurized crew compartments, remote-controlled gun turrets, and a separate pressurized tunnel connecting the forward and rear crew areas. Those features represented a major advance over the earlier B-17 Flying Fortress.
The prototype first flew on September 21, 1942. After testing and changes, the aircraft entered production as the B-29 Superfortress. It became the most advanced bomber operated by the United States during World War II and was used extensively in the Pacific theater.
The designation is easy to confuse with Model 299, the Boeing prototype that led to the B-17. Model 367 refers to the C-97 Stratofreighter, another important Boeing aircraft developed after the war. The B-29’s military designation therefore identifies the production bomber, while Model 345 identifies its Boeing design.