10 June 1969: The U.S. Air Force donated the first North American Aviation X-15, serial number 56-6670, to the Smithsonian Institution for display at the National Air and Space Museum. The first of three X-15A hypersonic research rocketplanes built by North American for the Air Force and the National Advisory Committee (NACA, the predecessor of NASA), 56-6670 made the first glide flight and