Aiming point

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An aiming point is a reference used to point field guns at targets you can’t see directly. It provides a point of direction (azimuth) to aim the gun in the right horizontal direction. For indirect fire, aiming points were essential because the gun’s line of sight isn’t on the target.

The aiming point must be far enough from the gun so the gun and its sights don’t move the aiming reference as they fire. If the aiming point is too close, small gun movements can change the aim, sometimes by hundreds of meters. A distance of a few kilometers is usually enough.

A good aiming point is a clearly visible feature, like the edge of a building. But in flat or featureless terrain, bad visibility, or at night, a distant aiming point is hard to see. So engineers developed ways to simulate a distant aiming point.

Early methods included two aiming posts about 50 meters from the gun; the sight could be aimed midway between them. The French introduced the collimateur before World War I. During the war, the British used a horizontal mirror called the paralloscope. In the 1950s the parallescope was replaced by a more robust prism parallescope. In the 1970s the United States introduced a modern version called the collimator. Infrared beacons were explored but had limited use.

In some cases, such as firing only one round or a single volley, a director or aiming circle about 100 meters away could serve as the aiming point.

Originally, aiming points helped quickly orient all guns to the same direction. Later, additional aiming points were used while firing, called gun aiming points (GAP). Some guns recorded GAP angles on plates or followed priority rules for which GAP to use. By the 1980s, the US Multi-Launch Rocket System did not need GAPs because it used a gyroscopic orientation system.

In the 1990s, similar systems were adopted for howitzers and self-propelled guns, including the M109 Paladin, AS90, Panzerhaubitze 2000, and later for towed guns like the UK's 105mm L118.