Leveling off at 42,000 feet, I had thirty percent of my fuel, so I turned on rocket chamber three and immediately reached .96 Mach. I noticed that the faster I got, the smoother the ride. Suddenly the Mach needle began to fluctuate. It went up to .965 Mach – then tipped right off the scale … We were flying supersonic. And it was a smooth as a baby’s bottom; Grandma could be sitting up there sipping lemonade.
Chuck Yeager, who broke the sound barrier on October 14, 1947
