What it was like to fly the baddest airplane the world has ever known
> 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.