Photographed outside their hangar at the Dryden Flight Research Center, Edwards, California, part of Dryden's F-16 fleet is, left to right; an F-16A, the F-16XL no. 1, and the F-16 AFTI. The F-16A (NASA 516), the only civil registered F-16 in existence, was transferred to Dryden from Langley, and is primarily used in engine tests and for parts. Although it is flight-worthy, it is not currently flown at Dryden. The single-seat F-16XL no. 1 (NASA 849) was most recently used in the Cranked-Arrow Wing Aerodynamics Project (CAWAP) to test boundary layer pressures and distribution. Previously it had been used in a program to investigate the characteristics of sonic booms for NASA's High Speed Research Program. Data from the program will be used in the development of a high speed civilian transport. During the series of sonic boom research flights, the F-16XL was used to probe the shock waves being generated by a NASA SR-71 and record their shape and intensity. The Advanced Fighter Technology Integration (AFTI) F-16 was used to develop and demonstrate technologies to improve navigation and a pilot's ability to find and destroy enemy ground targets day or night, including adverse weather. Earlier research in the joint NASA-Air Force AFTI F-16 program demonstrated voice actuated controls, helmet-mounted sighting and integration of forward-mounted canards with the standard flight control system to achieve uncoupled flight.