Crossbow was a long-range cruise missile developed by the Air Force as an anti-radar missile. Powered by a small turbo-jet air-breathing engine, it had distinctive straight wings and a twin vertical tail, with a movable rudder only on the left vertical fin. It was air-launched from under-wing pylons on B-50 or B-47 bombers and used a passive multiple-frequency radar seeker to home in on hostile ground radar systems. Once it detected a target, it dived on it at near sonic speed and its warhead detonated on impact. Development began in 1953 as the B-67 and changed to GAM-67 in 1955 when the Air Force abandoned aircraft designations for guided missiles. The first successful prototype flight occurred in July 1956, and the first guided flight took place in May 1957. The program was cancelled in July 1957 because of technical and funding problems. At White Sands Proving Ground, the Air Force first tested Crossbow in September 1954, and before cancellation in 1957, a total of 19 were launched there.