At these speeds, even a supersonic rocket is no longer fast enough to be simply aimed at the target. The missile must "lead" the target to ensure the target is hit before the missile depletes its fuel. This means that the missile and target cannot be tracked by a single radar, increasing the complexity of the system. One part was well developed. By this point, the US had considerable experience with lead-calculating analog computers, starting with the British Kerrison Predictor and a series of increasingly capable U.S. designs.