design, but was replaced instead by the Lockheed XSR13-LP-1 solid rocket. This lowered the top speed from Mach 6 to Mach 4. In this form, the GAR-9 started ground firings in August 1961. For air-launch testing at supersonic speeds the Republic XF-103 had originally been proposed as a test platform, but this aircraft was cancelled before reaching the prototype stage. Instead, B-58 Hustler s/n 55-665 was modified to house the AN/ASG-18 radar in a large protruding radome that gave it the nickname "Snoopy", and in-flight launches started in May 1962. Development for YF-12 In 1960 Lockheed started development of the Lockheed YF-12 interceptor, as a lower-cost replacement for the F-108. The GAR-9/ASG-18 were moved to this project. The F-12 would have featured four flip-open internal weapons bays on the chines behind the cockpit, one of these filled with electronics. The F-12B bays were too small for the GAR-9, so the GAR-9B was developed with flip-out fins to reduce its diameter. It weighed . Test firings of the GAR-9A from the prototype F-12As resulted in six kills from seven launches, the lone miss due to a missile power failure (there were several non-guiding test launches as well). The missile was renamed AIM-47 in late 1962 as part of the transition to common naming for aerospace vehicles across the U.S. Department of Defense in 1962. The last launch was from a YF-12 flying at Mach 3.2 and an altitude of 74,400 feet (22,677 m) at a QB-47 target drone 500 feet (152 m) off the ground. In 1966, the F-12 project was cancelled just as the F-108 had been. Another project which expressed an interest in the design was the XB-70 Valkyrie, a bomber which could have carried the AIM-47 for self-defense. This aircraft was also cancelled after Soviet deployment of effective high-altitude surface-to-air missiles made high-altitude attacks on the Soviet Union impractical. Hughes had built 80 pre-production AIM-47 missiles. Legacy The AIM-47 was used as a base for the AIM-54 Phoenix (originally the AAM-N-11), intended for the General Dynamics F-111B. This project was also canceled in 1968, but the weapon system finally found a home on the F-14 Tomcat, entering service in the early 1970s. In 1966, the basic airframe was adapted with the seeker from the AGM-45 Shrike and the warhead from the Mk. 81 bomb to create the high-speed AGM-76 Falcon anti-radar missile, although this did not see service.