Williams went on to direct test programs for the new generation of jet aircraft, including Douglas D-558-2 Skyrocket, the first aircraft to fly at twice the speed of sound; the Bell X-5, which pioneered the variable-sweep wing; the Convair XF-92, which pioneered the delta wing, and the Century Series of supersonic aircraft which were the fruits of his research in supersonic flight. In January 1958, he became chairman of the Flight Test Steering Committee for the hypersonicNorth American X-15.[3] He was the author of many NASA technical papers, including "The Comparison of Flight Measurement of High-Speed Airplane Stability and Control Characteristics", which he presented in Brussels in August 1956, and "The X-15 Research Airplane Program", which was presented at the American Rocket Society Space Exploration Regional Meeting in San Diego, California, in 1958.[3]
In 1963, Williams became deputy associate administrator in the Office of Manned Space Flight at NASA Headquarters. He left NASA in April 1964, and became vice president and general manager of the Vehicle Systems Division at The Aerospace Corporation, in which capacity he was responsible for systems engineering and technical direction of the Project GeminiTitan II launch and Atlas-Agena target vehicles, the Titan III launch vehicles, and the USAF Manned Orbiting Laboratory, along with Aerospace Corporation activities at both the Eastern and Western Test Ranges. He returned to NASA Headquarters as chief engineer in 1975, a position he held until he retired in July 1982.[2]
Williams died at his home in Tarzana, California, on October 7, 1995. He was survived by his wife Helen Manning Williams; sons Charles M. Williams and Howard L. Williams; and daughter, Elizabeth Ann Powell.[1] On November 17, 1995, Kenneth J. Szalai, the director of the Dryden Flight Research Center renamed the Integrated Test Facility (ITF) there the Walter C. Williams Research Aircraft Integration Facility in his honor.[3]