Coast Artillery fire control system

In the U.S. Coast Artillery, the term fire control system was used to refer to the personnel, facilities, technology and procedures that were used to observe designated targets, estimate their positions, calculate firing data for guns directed to hit those targets, and assess the effectiveness of such fire, making corrections where necessary.

In brief, the fire control system in use from about 1900 through WW2 involved observers, often situated in base end stations, using optical instruments (like azimuth telescopes or depression position finders) to measure bearings and/or distances to targets (usually moving ships). Both horizontal and vertical base position finding systems were used. These observations were communicated to personnel in battery plotting rooms, who used a mechanical device called a plotting board to indicate the target's observed location on a map of the area. The red "1" on the diagram at right indicates this first stage of the fire control process.

Once several positions had been plotted for the target (blue circles on Figure 1 at left), plotting board operators estimated the position of the target at the instant a salvo, fired by the battery, was expected to land. This position was called the set forward point (green square in Figure 1), since it involved "setting forward" the target's expected position (assuming continued forward travel at the same speed and in the same direction) during two intervals of time: (1) the dead time between the time the observation had been made and the time the guns were actually fired at that target plus (2) the time of flight--the time the projectile spent in the air before hitting something. The set forward point was expressed in terms of firing data: a range (in yards) and an azimuth (a compass heading in degrees) at which the gun/s should be pointed by the gun crews in order to hit the target.

Before these firing data were sent to the guns, however, they were corrected for a variety of "non-standard conditions", like temperature (which affected the explosive power of the powder charge) or wind strength and direction (which affected the flight of the projectile). The red "2" in the diagram at right indicates this stage in the fire control process. Special devices, like the deflection board (for corrections in azimuth) or the range correction board (for corrections in range) were used to produce corrected firing data.

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Wikipedia