Supersonic flight is flight at or above the speed of sound. The speed of sound is 760 miles (1,223 kilometers) per hour in warm air at sea level. At a height of about 37,000 feet (11,278 kilometers), the speed of sound is only 660 miles (1,062 kilometers) per hour.
The first person credited with flying faster than the speed of sound is Major Charles E. (Chuck) Yeager (1923-) of the United States Air Force. In 1947, he "broke the sound barrier" (also known as "attaining Mach 1") at 60,000 feet (18,288 meters), while flying the Bell X-l rocket research plane. This plane had been carried aloft by a B-29 bomber and released at 30,000 feet (9,144 meters).
In 1949, the Douglas Skyrocket, flown by Gene May, became the first supersonic, jet-powered aircraft. The Skyrocket surpassed the speed of sound while flying at 26,000 feet (7,925 meters).
Source: Encyclopedia of Aviation, pp. 184-85.