In the U.S. Army Coast Artillery Corps, the term fire control system was used to refer to the personnel, facilities, technology and procedures that were used to observe designated targets, estimate th
In this plotting room, the table is a Whistler-Hearn plotting board. A range correction board is on the left rear of the table.
A conceptual diagram of the flow of fire control data in the Coast Artillery (in 1940). The set forward point of the target was generated by using the plotting board (1). This position was then corrected for factors affecting range and azimuth (2). Finally, fire was adjusted for observations of the actual fall of the shells (3), and new firing data were sent to the guns.
A series of observed positions (blue circles) establishes the likely track of the target. Using a plotting board, the set forward point is determined, based upon the target's observed course and speed and an assumption about when the gun is to be fired.
This example shows the relationship of steps in the fire control process playing out over time.
Depression range finder
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The depression range finder was a fire control device used to determine the target's position by observing range and bearing and to calculate firing solutions when gun laying in coastal artillery. It
Coast Artillery fire control system
…be used quickly, these had baselines of only a few feet, reducing their accuracy and maximum effective range. Vertical base rangefinding used a single depression position finder (DPF) mounted as high as possible above the water level; these were derived from similar British devices and adopted beginning in 1896. Along with the…
A Watkin depression position finder on a range dial in a position finding cell, Dover Castle, England
O represents the observer, at a distance OM above sea level (and the target on the sea). The range to the target is determined by taking the cotangent of the depression angle d times the height of the instrument OM, to yield the range MP. But due to the curvature of the Earth, the true range is MT. To achieve this, the DPF instrument adjusts the observer's height from OM to ON, and then correctly measures the range as NT. Alternatively, the depression angle could be adjusted to
An American DPF (left) and azimuth scope (right) in use
An American Warner-Swasey DPF, illustration from a 1910 manual