Base end station

Base end stations were used by the U.S Coast Artillery as part of fire control systems for locating the positions of attacking ships and controlling the firing of seacoast guns, mortars, or mines to defend against them.

A "true" base end station was one of a pair of stations at either end of a precisely measured (surveyed) baseline. Once simultaneous bearings from each base end station to a target were taken, since the distance between the stations (the baseline) was known, the range to the target from either station could be calculated through triangulation. If the target's bearing from each station was sent to a plotting room and input to a plotting board, the position of the target could be estimated and firing coordinates for a gun battery could be calculated.

Some base end stations were located in tall fire control towers (FCTs) Sometimes, the terms "base end station" and "fire control tower" were used interchangeably. In general, however, a fire control tower (FCT) was a structure built to raise one or more base end, spotting, or observation stations high above ground level. Some fire control towers contained several base end stations, one on top of another on different stories of the tower, with each station being at one end of a different baseline and being assigned primarily to a different gun battery in a harbor's defensive scheme. Other base end stations resembled pillboxes or small bunkers dug into the ground or on the surface overlooking coastal waters. Still others were camouflaged to resemble seaside homes or cottages. Some base end stations had anti-aircraft observation positions on their top levels, or harbor observation radar antennas on platforms above their roofs.

Almost all base end stations were equipped at least with an azimuth telescope (similar to a surveyor's theodolite) to enable them to sight accurate bearings to a target. In addition, some base end stations held a depression position finder (DPF) or a coincidence range finder (CRF) that could be used by itself (without reference to another station) to produce fire control data for the gun(s). Sometimes a space holding one of these instruments (if not located on a baseline and paired with a second station) was referred to simply as an observation station.

These stations were used between the 1890s and 1946. At the end of the war almost all of them were declared surplus and were sold off to public and private owners. More than 100 of these stations likely still survive today across the United States, as part of state preserves or under private ownership, although many have been razed to clear sites for new development.

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