In 1951, NACA Engineer Richard Whitcomb determined the area rule that explained transonic flow over an aircraft. The first uses of this theory were on the Convair F-102 project and the F11F Tiger. The F-102 was meant to be a supersonic interceptor, but it was unable to exceed the speed of sound, despite the best effort of Convair engineers. The F-102 had actually already begun production when this was discovered, so NACA engineers were sent to quickly solve the problem at hand. The production line had to be modified to allow the modification of F-102s already in production to allow them to use the area rule. (Aircraft so altered were known as "area ruled" aircraft.) The design changes allowed the aircraft to exceed Mach 1, but only by a small margin, as the rest of the Convair design was not optimized for this. As the F-11F was the first design to incorporate this during initial design, it was able to break the sound barrier without having to use afterburner.