I had always though the SR-71 was the fastest airplane, and it turns out I'm right (sorta). The X-15 isn't an airplane, apparently (hence why it's only referred

I had always though the SR-71 was the fastest airplane, and it turns out I'm right (sorta). The X-15 isn't an airplane, apparently (hence why it's only referred to as an aircraft). I'm not sure why but probably because it's just a rocket and it doesn't actually "breathe air", nor does it seem to be able to take off on it's own?