Fire control tower

A fire control tower is a structure located near the coastline, used to detect and locate enemy vessels offshore, direct fire upon them from coastal batteries, or adjust the aim of guns by spotting shell splashes.

The U.S. Coast Artillery fire control system included many fire control towers, which were used between about 1900 and the end of WW2.

A fire control tower usually contained several fire control stations, known variously as observation posts (OPs), base end stations, or spotting stations from which observers searched for enemy ships, fed data on target location to a plotting room, or spotted the fall of fire from their battery, so the aim of the guns could be adjusted. For example, the fire control tower at Site 131-1A contained one OP, two base end stations, and two spotting stations. A shorthand notation was used to identify the stations.

For instance, the top story of Site 131-1A was planned to contain base end station #3 and spotting station #3 for Battery #15. The overall plan document for the harbor defenses contained a list that linked the tactical numbers of all batteries to their names. That document also contained an organization chart that identified all the Command (C) and Group (G) codes, like "G3."

These towers were arrayed in networks along the coast on either side of the artillery batteries they supported. The number and height of the towers was determined by the range of the guns involved. Many fire control towers were also part of a harbor's antiaircraft warning system. Spotters occupied cramped "crow's nests" on the top floors of the towers that enabled them to lift a trapdoor in the tower's roof and scan the sky for approaching aircraft.

When an enemy surface craft was detected, bearings to it were measured from a pair of towers, using instruments like azimuth scopes or depression position finders. Since the distances along the line between the towers (called a baseline) had already been precisely measured by surveyors, the length of this baseline, plus the two bearing angles from two stations at the ends of the line (also called base end stations) to the target, could be used to plot the position of the target by a mathematical process called triangulation.

A fire control tower was usually five to ten stories tall, depending on the height of the site at which it was built and the area it had to cover. Often made of poured concrete, its lower floors were usually unoccupied and were capped by occupied observation levels. Staircases ran up to the lowest observation level, and wooden ladders were then used to climb to higher levels. But some fire control structures built atop coastal hills or bluffs only needed to be one- or two-story buildings, and were built of wood or brick. Sometimes these buildings were camouflaged as private homes, and were referred to as fire control "cottages."

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