After initial test flights in 1959, X-15s became the first aircraft to reach Mach 4, 5, and 6, and to operate well above 30,500 meters (100,000 feet).
After initial test flights in 1959, X-15s became the first aircraft to reach Mach 4, 5, and 6, and to operate well above 30,500 meters (100,000 feet).