The X-15 was not the first rocket-powered aircraft, but it is probably the best one ever built and flown. Before the first X-15 took flight in the late 1950s, the fastest speed airplanes had reached was Mach 3. The X-15 doubled that. And, remarkably, it also went on to fly into space more than a dozen times.
The US Air Force and NASA developed the X-15 to better understand flight under extreme conditions, including reentry through the Earth’s atmosphere. Yet more than half a century later, the exceptional plane still holds the world record for speed by a piloted, powered aircraft after William Knight flew the vehicle at Mach 6.70 in 1967.
The X-15 program also boasts an exclusive club of pilots—only a dozen aviators can claim to have flown the aircraft, which made 199 flights in total. (They were all men, given the era.) Before he landed on the Moon, Neil Armstrong flew seven X-15 missions between 1960 and 1962. The movie First Man vividly depicts one of these flights.