The area rule was immediately applied to a number of development efforts. One of the most famous of these developments was Whitcomb's personal work on the re-design of the Convair F-102 Delta Dagger, a U.S. Air Force jet fighter that was demonstrating performance considerably worse than expected. By indenting the fuselage beside the wings, and (paradoxically) adding more volume to the rear of the plane, transonic drag was considerably reduced and the intended Mach 1.2 design speed was reached. The culminating design of this research was the Convair F-106 Delta Dart, an aircraft which for many years was the USAF's primary all-weather interceptor. Despite having the same J57 engine as the F-102, the F-106 was nearly twice as fast.