Bell Aircraft built three of the original X-1s, plus an X-1A and X-1B, an X-1D. There was also an X-1E rebuilt from the X-1 #2. They flew a total of 214 flights between 1946-1958. This was a joint program among the NACA, the Air Force, and Bell Aircraft. The bullet-shaped, rocket-powered aircraft became the first airplane to break the sound barrier on Oct. 14, 1947. Flight research by the NACA continued through such advanced models as the X-1B and X-1E, providing a wealth of information for use in correlating from the X-1 #2 wind-tunnel data with actual flight data and for designing later high-performance aircraft.