Test pilot John Griffith

Test pilot John Griffith pokes his head out of an X-1 to chat with ground crew members. Although aircraft had not broken the sound barrier until the advent of the initial X-Plane, some munitions apparently had--hence, according to NASA, the fuselage of the X-1 had essentially the same shape as a .50-caliber machine gun bullet, which was known to be stable at supersonic speeds. Under the hood, the X-1 packed an XLR-11 rocket engine, fueled by liquid oxygen and a mixture of alcohol and water.