Chuck Yeager is the first person to travel faster than Mach 1, the speed of sound, in level flight. On October 14, 1947, Yeager broke the sound barrier flying the Bell X-1 at an altitude of 45,000 feet.
It is believed that the Messerschmitt Me 262, the first operational jet powered aircraft, was able to break the sound barrier during dives. There are numerous reports of pilots of sudden, strange aerodynamic behavior during dives that are consistent with the effects while breaking the sound barrier, plus a number of unexplained crashes during high speed dives. Pilots described it as the plane being hit with a large hammer, often resulting in damage to the plane.