During 199 flights between 1959 and 1968, the X-15 was one of the most remarkable of all the rocket research aircraft -- and the fastest piloted aircraft ever. The X-15 first set speed records in the Mach 4 to 6 range with Mach 4.43 in March 1961; Mach 5.27 in June 1961; Mach 6.04 in November 1961; and Mach 6.7 on October 3, 1967.

The X-15 also set an altitude record of 354,200 feet in August 1963, and gathered enormous amounts of data on hypersonic air flow, aerodynamic heating, control and stability at hypersonic speeds, reaction controls for flight above the atmosphere, piloting techniques for re-entry, human factors, and flight instrumentation of relevance not only to aeronautics but to spaceflight.