To reach the sound barrier in an airplane was a major goal for many in the aeronautical field, a goal that carried some uncertainties. Pilots and engineers alike wondered and feared what would happen to a plane’s maneuverability when it broke through the shock wave as well as what would happen to the plane itself, structurally.

Near the end of the Second World War there were fighter planes that were very strong and had powerful engines and experienced pilots. A number of pilots died when their planes broke apart in mid-air, often when in dives. There were two problems with these aircraft: first, the wings were not swept back, and second, they were driven by propellers. As the shock wave forms near Mach 1, it bends backward from the nose of the plane, like a bow wave on a boat. If the shock wave encounters the wings (that is, the wing extends through the shock front), there are tremendous forces on the wings. In a supersonic plane the wing is always designed to be fully behind the shock front, because the shock front can tear the wing off the plane. The propeller causes a pulsation in the pressure on the wing: every time one of the blades goes by, it produces a region of slightly higher pressure behind it, followed by a region of low pressure. All of these things came together and helped cause mid-air structural failures of the WWII fighter planes.