The SR-71 flys at more than three times the speed of sound at altitudes in excess of 80,000 feet (approximately 15 miles high). Three times the speed of sound (Mach 3) is more than 2,000 miles per hour or about 3,100 feet per second. By comparison, the muzzle velocity of a .30-06 rifle bullet is only 3,000 feet per second.