A modified Boeing NB-52 'mothership' carries the rocket-powered North American X-15 beneath its wing at Edwards Air Force Base. From 1959 to 1968, two specially adapted B-52s air-launched the X-15 at high altitude, enabling the experimental aircraft to reach speeds beyond Mach 6 and altitudes bordering space, generating data critical to later spaceflight and shuttle programs. Project: 218474