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. Fire control towers came into general use in coastal defence systems in the late 19th century, as rapid development significantly increased the range of both naval guns and coastal artillery. This made fire control more complex. These towers were used in a number of countries' coastal defence systems through 1945, much later in a few cases such as Sweden. The Atlantic Wall in German-occupied Europe during World War II included fire control towers.
The U.S. Coast Artillery fire control system included many fire control towers. These were introduced in the U.S. with the Endicott Program, and were used between about 1900 and the end of WWII. [lower-alpha 1]
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. [lower-alpha 2] That document also contained an organization chart that identified all the Command (C) and Group (G) codes, like "G3." [lower-alpha 3]
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. [lower-alpha 4] [1]
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." [lower-alpha 5]
The center of octagonal concrete mounting pad on the eight floor of 131-1A (which was meant to support a depression position finder) was usually the surveyed point at the end of the baseline (and thus the precise location of the base end station). [lower-alpha 6] A survey marker embedded in the tower's roof directly above this pad defined this point. Other observing instruments on lower floors of the tower were usually lined up directly beneath the eighth floor mounting pad and the rooftop marker, so they shared the same latitude and longitude. The pipe stands shown on floors six and seven of the Nahant Site 131-1A tower probably held azimuth scopes, which were less complex telescopes that determined bearings to a target but not its range from the tower.
Site 131-1A had electric lights, phones, and radio communications, and a time interval bell that was used for coordinating fire control information. Some fire control towers were also the mounting points for coast surveillance or fire control radar antennas. Although our sample tower has a simple, square appearance, some versions of these towers in New England had round or partly octagonal plans.
Each major battery of Coast Artillery guns was supported by a network of fire control structures (towers, cottages, or buildings) which were spread out along the nearby coast. [lower-alpha 7] Guns of longer range had larger numbers of fire control stations in their networks. Depending on where the target ship was located and upon other tactical conditions, one or more of these stations would be selected to control the fire from a given battery on that target.
For a WW2-era example, take Battery Murphy, the two 16-inch (406 mm) guns in Nahant, MA. Murphy used ten fire control stations that made up Battery Murphy's fire control network, which was spread out over about forty miles of coastline running from Station 1 (Fourth Cliff) in the south to Station 10 (Castle Hill) in the north. Half of these stations were located in tall towers, and half in low-rise cottages.
The length of the baselines running between each pair of stations was known very precisely. For example, Station #1 and Station #2 were 12,249.63 yards (6.96 mi; 11.2 km) apart. These distances were plugged into the triangulation equations for the pair of stations involved in sighting on a particular target in order to compute its position. [lower-alpha 8] As the target ship moved along the coast, different pairs of fire control stations (and therefore different baselines) would come into play. Very precise measurements were also taken of the distance between the directing point of each battery (often the pintle center of its Gun #1) and each fire control station's observing point. These distance could also be used for target location, if one of the observations was taken from the battery itself and another from the distant station.
Coastal artillery is the branch of the armed forces concerned with operating anti-ship artillery or fixed gun batteries in coastal fortifications.
Base end stations were used by the United States Army Coast Artillery Corps 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 British equivalent was the position finding cell.
Battery John Gunnison, known as Battery New Peck following its modernization in 1943, is a six-inch US Army coast artillery gun emplacement located at Fort Hancock in New Jersey.
East Point Military Reservation was a World War I and World War II coastal defense site located in Nahant, Massachusetts. In 1955–62 it was a Nike missile launch site. In 1967 the site was converted into the Marine Science Center of Northeastern University.
Salisbury Beach Military Reservation was a coastal defense site located in Salisbury, Massachusetts.
Coastal defenceand coastal fortification are measures taken to provide protection against military attack at or near a coastline, for example, fortifications and coastal artillery. Because an invading enemy normally requires a port or harbour to sustain operations, such defences are usually concentrated around such facilities, or places where such facilities could be constructed. Coastal artillery fortifications generally followed the development of land fortifications, usually incorporating land defences; sometimes separate land defence forts were built to protect coastal forts. Through the middle 19th century, coastal forts could be bastion forts, star forts, polygonal forts, or sea forts, the first three types often with detached gun batteries called "water batteries". Coastal defence weapons throughout history were heavy naval guns or weapons based on them, often supplemented by lighter weapons. In the late 19th century separate batteries of coastal artillery replaced forts in some countries; in some areas these became widely separated geographically through the mid-20th century as weapon ranges increased. The amount of landward defence provided began to vary by country from the late 19th century; by 1900 new US forts almost totally neglected these defences. Booms were also usually part of a protected harbor's defences. In the middle 19th century underwater minefields and later controlled mines were often used, or stored in peacetime to be available in wartime. With the rise of the submarine threat at the beginning of the 20th century, anti-submarine nets were used extensively, usually added to boom defences, with major warships often being equipped with them through early World War I. In World War I railway artillery emerged and soon became part of coastal artillery in some countries; with railway artillery in coast defence some type of revolving mount had to be provided to allow tracking of fast-moving targets.
Fort Andrews was created in 1897 as part of the Coast Defenses of Boston, Massachusetts. Construction began in 1898 and the fort was substantially complete by 1904. The fort was named after Major General George Leonard Andrews, an engineer and Civil War commander, who assisted in the construction of nearby Fort Warren in Boston Harbor. It occupies the entire northeast end of Peddocks Island in Boston Harbor, and was originally called the Peddocks Island Military Reservation. Once an active Coast Artillery post, it was manned by hundreds of soldiers and bristled with mortars and guns that controlled the southern approaches to Boston and Quincy Bay. The fort also served as a prisoner-of-war camp for Italian prisoners during World War II, who were employed as laborers following the Italian surrender to the Allies in 1943. Today, the fort is abandoned, and is managed by the Massachusetts Department of Conservation and Recreation, as part of the Boston Harbor Islands National Recreation Area.
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.
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 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. 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, 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. Locations of plotting rooms in coastal defence installations varied greatly; they could be in low-rise structures such as base end stations, taller fire control towers, in gun battery structures, or in bunkers separate from gun batteries.
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.
Fort Heath was a US seacoast military installation for defense of the Boston and Winthrop Harbors with an early 20th-century Coast Artillery fort, a 1930s USCG radio station, prewar naval research facilities, World War II batteries, and a Cold War radar station. The fort was part of the Harbor Defenses of Boston and was garrisoned by the United States Army Coast Artillery Corps. The fort's military structures have been replaced by a residential complex, including the luxurious Forth Heath Apartments, and recreation facilities of Small Park, which has both a commemorative wall and an historical marker for Fort Heath.
The modern era of defending American harbors with controlled mines or submarine mines began in the post-Civil War period, and was a major part of US harbor defenses from circa 1900 to 1947.
Fort Duvall was a Coast Artillery fort, part of the Harbor Defenses of Boston, in Massachusetts. What was then called Hog Island in Hull, Massachusetts was acquired by the U.S. government in 1917, and the fort was constructed in the early 1920s. It had only one gun battery, Battery Long, but it mounted the largest caliber weapons in the entire harbor defense system: a pair of 16-inch guns. These were the 16-inch gun M1919, of which only seven were deployed; 16-inch weapons deployed later were supplied by the Navy.
Fort Ruckman was a U.S. Coast Artillery fort located in Nahant, Massachusetts. Originally called the Nahant Military Reservation, the fort was laid out in 1904-1907 and covered an area of about 45 acres just northwest of Bass Point, on the southwest side of the Nahant peninsula. During the 1920s, this area was renamed in honor of Maj. Gen. John Wilson Ruckman, a former Colonel in the Coast Artillery.
Fort Dawes was a World War II Coast Artillery fort located on Deer Island in Winthrop/Boston, Massachusetts. It was part of the Harbor Defenses of Boston.
Fort Foster, now part of Fort Foster Park, is a historic fort active 1901–1946 on the southwest tip of Gerrish Island in the Kittery Point area of Kittery, Maine. The park includes beaches and trails. Battery Bohlen and Battery Chapin were the major parts of the fort.
Fort Greene is a United States Army Reserve installation in the Point Judith area of Narragansett, Rhode Island. During World War II this was a coastal defense fort, and together with Fort Church in Little Compton, it superseded all previous heavy gun defenses in the Harbor Defenses of Narragansett Bay. It is named for General Nathanael Greene of the Revolutionary War, who was born in Rhode Island.
The Harbor Defenses of Portsmouth was a United States Army Coast Artillery Corps harbor defense command. It coordinated the coast defenses of Portsmouth, New Hampshire and the nearby Portsmouth Naval Shipyard in Kittery, Maine from 1900 to 1950, both on the Piscataqua River, beginning with the Endicott program. These included both coast artillery forts and underwater minefields. The command originated circa 1900 as the Portsmouth Artillery District, was renamed Coast Defenses of Portsmouth in 1913, and again renamed Harbor Defenses of Portsmouth in 1925.
The Harbor Defenses of Boston was a United States Army Coast Artillery Corps harbor defense command. It coordinated the coast defenses of Boston, Massachusetts from 1895 to 1950, beginning with the Endicott program. These included both coast artillery forts and underwater minefields. The command originated circa 1895 as the Boston Artillery District, was renamed Coast Defenses of Boston in 1913, and again renamed Harbor Defenses of Boston in 1925.
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.