On June 29th,  1965 Captain Joe H. Engle flew 56-6672 for his 12th X-15 flight and the 138th flight of the X-15 Program. He fired the engine for 81.0 seconds and accelerated to Mach 4.94 (3,432 miles per hour, 5,523 kilometers per hour). The X-15 climbed to an altitude of 280,600 feet (85,527 meters, 53.14 miles). He touched down at Edwards Air Force Base after 10 minutes, 34.2 seconds of flight. Captain Engle qualified for Astronaut wings on this flight, the third and youngest Air Force pilot to do so. This design is inspired by that same aircraft.