Plotting room

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In this U.S. Army Coast Artillery Corps plotting room, the table is a Whistler-Hearn plotting board. Other devices for fire control are visible on the table. Plotting room - Whistler-Hearn plotting board.jpg
In this U.S. Army Coast Artillery Corps plotting room, the table is a Whistler-Hearn plotting board. Other devices for fire control are visible on the table.
Cut-away view of a Royal Navy World War II K-class destroyer Director Control Tower (D.C.T.) with Type 285 radar; plotting room shown on lower level Radar and Electronic Warfare 1939-1945 A28824.jpg
Cut-away view of a Royal Navy World War II K-class destroyer Director Control Tower (D.C.T.) with Type 285 radar; plotting room shown on lower level
This massive concrete casemate housed the underground plotting room for the 12-inch mortars of Battery Whitman at Fort Andrews in Boston Harbor. Plotting room casemated.jpg
This massive concrete casemate housed the underground plotting room for the 12-inch mortars of Battery Whitman at Fort Andrews in Boston Harbor.
1904 fire control station, east side of Fort Andrews, Massachusetts East Side FC Station.jpg
1904 fire control station, east side of Fort Andrews, Massachusetts
Plan of fire control station, east side of Fort Andrews, Massachusetts East FC Plan 1904.jpg
Plan of fire control station, east side of Fort Andrews, Massachusetts

A plotting room was the co-ordination centre of a fire control system for guns used against enemy ships or aircraft, whether naval guns or coastal artillery. The plotting room received data on ship or aircraft position and motion from fire control instruments or their operators and determined and transmitted the range and bearing (a.k.a. azimuth or deflection) the guns would fire on. Plotting rooms came into use in the early 1900s for coastal artillery and during World War I for warships as gun ranges increased, and were in general use through the 1970s on World War II-era ships (and into the 1990s on the US Navy's Iowa-class battleships). [1] [2] Warships had plotting rooms for naval fire control for guns from 5-inch to 18-inch calibre, including anti-aircraft use for the smaller guns. On armoured ships such as battleships and cruisers, plotting rooms were located in the armoured citadel, protected by both deck and belt armour. With a few exceptions (mostly in Scandinavia), coastal defence gun installations were inactivated shortly after World War II (US) through the middle 1950s (UK). Equipment in plotting rooms included specialised plotting boards and other analogue devices; by World War II these were supplemented or replaced by electro-mechanical gun data computers. Data could be received and transmitted by telephone, or directly via dedicated electrical systems. [3] Locations of plotting rooms in coastal defence installations varied greatly; they could be in low-rise structures such as base end stations (usually colocated with observation equipment in a two-story structure), taller fire control towers, in gun battery structures, or in bunkers separate from gun batteries. [2]

Contents

The British Watkin position finder system for coastal artillery, which entered service in the 1890s, did not require a plotting room due to mounting a depression position finder (DPF) on a "range dial", similar to a plotting board. An electrical system moved bearing and range dials near the guns as the DPF was manipulated by an operator. [4] [5] [6]

See also

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A plotting board was a mechanical device used by the U.S. Army Coast Artillery Corps as part of their fire control system to track the observed course of a target, project its future position, and derive the uncorrected data on azimuth and range needed to direct the fire of the guns of a battery to hit that target. Plotting boards of this sort were first employed by the Coast Artillery around 1905, and were the primary means of calculating firing data until WW2. Towards the end of WW2 these boards were largely replaced by radar and electro-mechanical gun data computers, and were relegated to a back-up role.

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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 their positions, calculate firing data for guns directed to hit those targets, and assess the effectiveness of such fire, making corrections where necessary.

<span class="mw-page-title-main">Depression range finder</span>

The depression range finder (DRF) 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 was the main component of a vertical base rangefinding system. It was necessitated by the introduction of rifled artillery from the mid-19th century onwards, which had much greater ranges than the old smoothbore weapons and were consequently more difficult to aim accurately. The DRF was invented by Captain H.S.S. Watkin of the Royal Artillery in the 1870s and was adopted in 1881. It could provide both range and bearing information on a target. The device's inventor also developed a family of similar devices, among them the position finder, which used two telescopes as a horizontal base rangefinding system, around the same time; some of these were called electric position finders. Some position finders retained a depression range finding capability; some of these were called depression position finders. Watkin's family of devices were deployed in position finding cells, a type of fire control tower, often in configurations that allowed both horizontal base and vertical base rangefinding. Watkin's system included automatic electrical updating of range and bearing dials near the guns as the position finders were manipulated, and a system of remotely firing the guns electrically from the position finding cell. The improved system was trialled in 1885 and widely deployed in the 1890s. Functionally equivalent devices were developed for the United States Army Coast Artillery Corps and its predecessors, called depression position finders or azimuth instruments depending on function, adopted in 1896 and deployed widely beginning in the early 1900s as the Endicott program of modern coastal defences was built. These devices were also used by both countries to control submarine (underwater) minefields.

References

  1. "FM 4-15, Seacoast Artillery fire control and position finding". Archived from the original on 2019-05-02. Retrieved 2019-05-12.
  2. 1 2 Berhow, Mark A., ed. (2015). American Seacoast Defenses, A Reference Guide (Third ed.). McLean, Virginia: CDSG Press. pp. 263–283. ISBN   978-0-9748167-3-9.
  3. Naval Ordnance and Gunnery, Volume 2, Fire Control, NAVPERS 10798-A. Washington, DC: U.S. Navy, Bureau of Naval Personnel. 1958.
  4. Coast defence range finding at victorianforts.co.uk
  5. Major Watkin's Position Finder at victorianforts.co.uk
  6. Watkin depression position finders at victorianforts.co.uk