Director (military)

A director, also called an auxiliary predictor, is a mechanical or electronic computer that continuously calculates trigonometric firing solutions for use against a moving target, and transmits targeting data to direct the weapon firing crew.

For warships of the 20th century, the director is part of the fire control system; it passes information to the computer that calculates range and elevation for the guns. Typically, positions on the ship measured range and bearing of the target; these instantaneous measurements are used to calculate rate of change values, and the computer ("fire control table" in Royal Navy terms) then predicts the correct firing solution, taking into account other parameters, such as wind direction, air temperature, and ballistic factors for the guns. In World War II a widely used computer in the US Navy was the electro-mechanical Mark I Fire Control Computer.

On ships the director control towers for the main battery are placed high on the superstructure, where they have the best view. Due to their large size and weight, in the World War II era the computers were located in plotting rooms deep in the ship, below the armored deck on armored ships.

Directors were introduced into field artillery in the early 20th century to orient the guns of an artillery battery in their zero line (or 'centre of arc'). Directors were an essential element in the introduction of indirect artillery fire. In US service these directors were called 'aiming circles'. Directors could also be used instead of theodolites for artillery survey over shorter distances. The first directors used an open sight rotating on an angular scale (e.g. degrees & minutes, grads or mils of one sort or another), but by World War I most directors were optical instruments. Introduction of digital artillery sights in the 1990s removed the need for directors.

Directors were mounted on a field tripod and oriented in relation to grid north of the map. If time was short this orientation usually used an integral compass, but was updated by calculation (azimuth by hour angle or azimuth by Polaris) or 'carried' by survey techniques from a survey control point. In the 1960s gyroscopic orientation was introduced.

For anti-aircraft use, directors are usually used in conjunction with other fire control equipment, such as height finders or fire control radars. In some armies these 'directors' were called 'predictors'. The Mark 51 director was used by the US Navy for 40 mm guns and later for 3"/50 caliber guns. The Kerrison Predictor was also designed to use with the Bofors 40 mm gun.

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