Chuck Yeager was first to do so on 14 October 1947 in the Bell X-1. , Yeager's craft was powered by a rocket engine. However, another flight test program that was in progress at Muroc Field (now Edwards Air Force Base) during the same time period was that of the jet-powered XP-86, prototype of the F-86 Sabre soon to gain fame in the Korean War.
Shortly before the X-1's famous flight, North American test pilot George Welch had been conducting high-speed dives of the XP-86. During these flights, he had noticed odd behavior of the aircraft's speed indicator which jumped erratically as he approached Mach 1. Later on, this phenomenon would come to be known as "Mach jump" and is indicative of encountering shock waves at transonic speeds near the speed of sound. Witnesses on the ground had also reported hearing the tell-tale "BA-BOOM" sound indicative of the sonic boom created by a supersonic vehicle