1947 -- Breaking the Sound Barrier On Oct. 14, 1947, Capt. Charles E. Yeager in the Bell X-1 rocket-propelled experimental aircraft was the first man to exceed the speed of sound in level flight, crossing with little trouble an invisible threshold thought to be an impediment to aircraft development and to contemporary aircraft structures. Yeager was awarded a cluster to his Distinguished Flying Cross; the Mackay Trophy, given annually by the National Aeronautic Association for the outstanding flight of the year; and the Collier Trophy given annually for achievement in aeronautics. In its successful conduct of the XS-1 program, from Ezra Kotcher's original conceptualization through Yeager's milestone flight, the U.S. Air Force had demonstrated that the military could play a very meaningful role in experimental flight research. See the Smithsonian National Air and Space Museum.