Artillery spotting

A military artillery observer or spotter or FO (forward observer) is responsible for directing artillery and mortar fire onto a target, and may be a Forward Air Controller (FAC) for close air support and spotter for naval gunfire support. Also known as "Fire Support Specialist" or "FISTer", an observer usually accompanies a tank or infantry manoeuvre unit. More recently a mission controller for an Army Unmanned Air System (UAS) may also perform this function, and some armies use special artillery patrols behind the enemy's forward elements. Spotters ensure that indirect fire hits targets which the troops at the fire support base cannot see.

Broadly, there are two very different approaches to artillery observation. Either the observer has command authority and orders fire, including the type and amount of ammunition to be fired, to batteries. Or the observer requests fire from an artillery headquarters at some level, which decides if fire will be provided, by which batteries, and the type and amount of ammunition to be provided. The first is characterised by the British, the second by the United States. In World War II both Germany and the Soviet Union tended towards the British method.

Because artillery is an indirect fire weapon system, the guns are rarely in line-of-sight of their target, often located miles away. The observer serves as the eyes of the guns, by sending target locations and if necessary corrections to the fall of shot, usually by radio.

In the US System the observer sends a request for fire, usually to his battalion or battery Fire Direction Center (FDC). The FDC then decides how much fire to permit and may request additional fire from a higher artillery headquarters. FDC(s) convert the observer's target information into firing data for the battery's weapons.

In the British system the observer sends a fire order to his own and any other batteries authorised to them, and may request fire from additional batteries. Each battery command post converts the fire orders into firing data for its own guns. Until post-World War II the observer would usually order actual firing data to the guns of his own troop, this was enabled by the use of calibrating sights on the guns.

On land, artillery observers are considered high-priority targets by enemy forces, as they control a great amount of firepower, are within visual range of the enemy, and may be located within enemy territory.

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