The Hughes AN/ASG-18 fire control system was a prototype airborne radar/combination system for the planned North American XF-108 Rapier interceptor aircraft for the United States Air Force, and later for the Lockheed YF-12. The US's first pulse-Doppler radar, the system had look-down/shoot-down capability and could track one target at a time. Flight tests of the AN/ASG-18 system, using a modified Convair B-58, began in 1960. During the 1960s, YF-12 flight tests were conducted, which included the use of the YF-12's onboard AN/ASG-18 radar system in conjunction with AIM-47 missiles to shoot down target drones.