The world's fastest aircraft. An X-15 under the wing of NASA's B-52 air-launching aircraft. The X- 15 was a rocket-powered aircraft designed to investigate flight at hypersonic speeds. Three X- 15s flew a total of 199 missions between 1959 and 1968. After take-off, the B-52 would climb to high altitude before releasing the X-15. The X-15 pilot would then ignite the aircraft's rocket motor. This would propel the X-15 to speeds of 7274 km/h (Mach 6.7) and altitudes of 107,960 metres (67 miles). These figures still stand as world records (1992) - the Space Shuttle being classified as a spacecraft. The Shuttle programme benefited greatly from the X-15 programme.