The XB-70 was conceived in 1954 as a subsonic bomber capable of short supersonic dashes. In December of 1957, North American won a competition with Boeing for development of the new bomber. The government decided to build only two of this aircraft, and they were to be used purely for high-speed research. During the testing program, the second Valkyrie was lost in a midair collision. The first Valkyrie was then re-instrumented and served as a flying laboratory for the American Supersonic Transport program and in 1969 it was delivered to the US Air Force Museum.