As the US forces digested the implication of German aerodynamic research at the end of the Second World War, a number of important new avenues were opened to them. The US Navy was particularly impressed with the tailless delta platform, which seemed to offer great potential for jet powered interceptor needed a high rate of climb and good performance at altitude. In 1947 the US Navy contracted with Douglas for initial work into such a machine, and in December 1948 ordered two XF4D-1 prototypes. The first of these flew in January 1951 with a 5,000-b thrust Allison J35A-17 turbojet as the planed Westinghouse J40 was not ready. Powered by an XJ40-WE-8, the second prototype set a world absolute speed record of 752.9 mph. in October 1953, and the F4D-1 production type with Pratt & Whitney engine set several world time to height records. The type entered service in April 1956, and the last of 419 aircraft was delivered in December 1958. The F4D-1 equipped 17 USN US Marine Corps squadrons as well as three USN reserve squadrons, most of them land based for continental defense. The type was redesigned F6A in 1962, and remained in first line service up to the late 1960s.