As early as 1946, the Air Force recognized the need to eventually develop a fast intercontinental-range bomber. Boeing and Convair went head-to-head demonstrating bomber prototypes (a Douglas turboprop–powered proposal never moved off the drawing boards). Boeing's design was ultimately accepted by the Air Force, and Boeing was authorized to build two aircraft, the XB-52 and YB-52. Estimated top speed was more than 600 mph with a range far greater than that of the medium-range B-47s.