On October 14, 1947, with USAF Captain Charles Chuck Yeager as pilot, the X-1-1 flew faster than the speed of sound for what is generally accepted as the first supersonic flight by a piloted aircraft.

Captain Yeager ignited the four-chambered XLR-11 rocket engines after being air-launched from under the bomb bay of a JTB-29A at 21,000 feet. The 6,000-pound thrust ethyl alcohol/liquid oxygen burning rockets pushed him up to a speed of Mach 1.06 at an altitude of 45,000 feet.