The wedge-shaped vertical stabilizer necessary for directional stability, upper speed brakes and a small tail-skid in retracted position is visible on the first X-15 on display at NASM. Just three of these hypersonic aircraft were built, and only 12 pilots flew them including Neil Armstrong for a total of 199 flights from 1959-68. The X-15 set the world's unofficial speed record of Mach 6.70 with Flight No. 2-53-97, and an altitude record of 354,200 ft. with Flight No. 3-22-36. The second X-15 is displayed at NMUSAF. The third X-15 was lost on 15 Nov 1967 on Flight 3-65-97 in a fatal accident.

The first of the three X-15's - also referred to as the X-15-1. Launched from the B-52 carriers, this rocket-powered research aircraft reached over Mach 5 and 50 miles altitude. The pilots of those particular flights being classified by the Americans as astronauts.

The first of three X-15 research aircraft is pictured on display in the Air and Space Museum's Milestones of Flight foyer. This aircraft conducted 82 of the 199 powered flights in the X-15 program. The second aircraft is displayed at the National Museum of the United States Air Force in Dayton, OH and the third was lost during testing.