Counterbattery radar was commonly employed at firebases. One typical example was the AN/MPQ-4A, which emitted two radio beams. If an enemy projectile broke the beams within a 6-mile distance, it would appear on a scope and then a computer would determine the approximate coordinates of the shot’s origin. This AN/MPQ-4A was at the Song Be base in the Central Highlands in January 1968. (U.S. Army)