A counter-battery radar, weapon locating radar or weapon tracking radar is a radar system that detects artillery projectiles fired by one or more guns, howitzers, mortars or rocket launchers and, from their trajectories, locates the position on the ground of the weapon that fired it. Such radars are a subclass of the wider class of target acquisition radars.

Early counter-battery radars were generally used against mortars, whose lofted trajectories were highly symmetrical and allowed easy calculation of the launcher's location. Starting in the 1970s, digital computers with improved calculation capabilities allowed more complex trajectories of long-range artillery to also be determined. Normally, these radars would be attached to friendly artillery units or their support units, allowing them to quickly arrange counter-battery fire.

With the aid of modern communications systems, the information from a single radar can be rapidly disseminated over long distances. This allows the radar to notify multiple batteries as well as provide early warning to the friendly targets. Modern counter-battery radar can locate hostile batteries up to about 50 kilometres (31 mi; 27 nmi) away depending on the radar's capabilities and the terrain and weather. Some counter-battery radars can also be used to track the fire of friendly artillery and calculate corrections to adjust its fire onto a particular place, but this is usually a secondary mission objective.

Radar is the most recently developed means of locating hostile artillery. The emergence of indirect fire in World War I saw the development of sound ranging, flash spotting and aerial reconnaissance, both visual and photographic. Radars, like sound ranging and flash spotting, require hostile guns, etc., to fire before they can be located.

The first radars were developed for anti-aircraft purposes just before World War II. These were soon followed by fire control radars for ships and coastal artillery batteries. The latter could observe the splashes of water from missing shots, enabling corrections to be plotted. Generally, the shells could not be seen directly by the radar, as they were too small and rounded to make a strong return, and travelled too quickly for the mechanical antennas of the era to follow.

Radar operators in light anti-aircraft batteries close to the front line found they were able to track mortar bombs. This was likely helped by the fins of the bomb producing a partial corner cube that strongly reflected the signal. These accidental intercepts led to their dedicated use in this role, with special secondary instruments if necessary, and development of radars designed for mortar locating. Dedicated mortar-locating radars were common starting in the 1960s and were used until around 2000.

Locating mortars was relatively easy because of their high, arcing, trajectory. At times, just after firing and just before impact, the trajectory is almost linear. If a radar observes the shell at two points in time just after launch, the line between those points can be extended to the ground and provides a highly accurate position of the mortar, more than enough for counter-battery artillery to hit it with ease. Better radars were also able to detect howitzers when firing at high angles, elevations greater than 45°, although such use was quite rare.

Low angle trajectories normally used by guns, howitzers and rockets were more difficult. Purely ballistic low-angle trajectories are lopsided, being relatively parabolic for the start of the flight but becoming much more curved near the end. This is further modified by otherwise minor effects like wind, air pressure differences and aerodynamic effects, which have time to add up to a noticeable effect on long-range fire but can be ignored for short-range systems like mortars. These effects are minimized immediately after launch, but the low angle makes it difficult to see the rounds during this time, in contrast to a mortar which climbs above the horizon almost immediately. Adding to the problem is the fact that traditional artillery shells make for difficult radar targets.