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25-619: The Elizabeth Islands Military Reservation was built on land acquired by the US government in 1943. It consisted of an early radar, an observation post, fire control towers , and artillery batteries. The reservation had two Anti-Motor Torpedo Boat (AMTB) batteries of four 90 mm guns each, AMTB 932 on the northern tip of Cuttyhunk and AMTB 933 on Fox Point, Nashawena. Each battery had an authorized strength of four 90 mm guns, two on fixed mounts and two on towed mounts, plus two towed 37 mm M1 guns or 40 mm Bofors M1 guns. These were mirrored across

50-406: 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

75-453: A particular target in order to compute its position. 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

100-495: A station mark that had been disturbed or destroyed. Some old station marks were buried several feet down (to protect them from being struck by ploughs). Occasionally, these buried marks had surface marks set directly above them. In the U.S., survey marks that meet certain standards for accuracy are part of a national database that is maintained by the National Geodetic Survey (NGS), the successor agency to

125-483: Is the hobby of "hunting" for these marks. All sorts of different objects, ranging from the familiar brass disks to liquor bottles, clay pots, and rock cairns , have been used over the years as survey markers. Some markers have been used to designate tripoints , or the meeting points of three or more countries. In the 19th century, these marks were often drill holes in rock ledges, crosses or triangles chiseled in rock, or copper or brass bolts sunk into bedrock. Today in

150-486: The United States Coast and Geodetic Survey (USC&GS). Each station mark in the database has a PID (Permanent IDentifier), a unique 6-character code that can be used to call up a datasheet describing that station. The NGS has a web-based form that can be used to access any datasheet, if the station's PID is known. Alternatively, datasheets can be called up by station name. A typical datasheet has either

175-475: The U.S. with the Endicott Program , and were used between about 1900 and the end of WWII. 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

200-744: The United States, the most common geodetic survey marks are cast metal disks with stamped legends on their face set in rock ledges, embedded in the tops of concrete pillars, or affixed to the tops of pipes that have been sunk into the ground. These marks are intended to be permanent, and disturbing them is generally prohibited by federal and state law. Survey markers in Nagoya, Japan, which bear stylized images of shachihoko , are noted for their elaborate design. Survey markers were often placed as part of triangulation surveys, measurement efforts that moved systematically across states or regions, establishing

225-690: 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

250-448: The angles and distances between various points. Such surveys laid the basis for map-making across the world. Geodetic survey markers were often set in groups. For example, in triangulation surveys, the primary point identified was called the triangulation station, or the "main station". It was often marked by a "station disk" (see upper photo at left), a brass disk with a triangle inscribed on its surface and an impressed mark that indicated

275-568: The channel by a single 90 mm AMTB battery at the Barneys Joy Point Military Reservation . Both islands were disarmed in 1946. The site today consists of the foundations of the various buildings and gun blocks. Two fire control towers also remain standing. 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

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300-420: 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). 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

325-410: 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

350-616: 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." The center of octagonal concrete mounting pad on

375-444: The latitude and longitude of the station mark, a listing of any reference marks (with their distance and bearing from the station mark), and a narrative (which is updated over the years) describing other reference features (e.g., buildings, roadways, trees, or fire hydrants) and the distance and/or direction of these features from the marks, and giving a history of past efforts to recover (or re-find) these marks (including any resets of

400-420: 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

425-499: The marks, or evidence of their damage or destruction). Current best practice for stability of new survey markers is to use a punch mark stamped in the top of a metal rod driven deep into the ground, surrounded by a grease filled sleeve, and covered with a hinged cap set in concrete. Survey markers are now often used to set up a GPS receiver antenna in a known position for use in Differential GPS surveying. In Brazil,

450-557: 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. Guns of longer range had larger numbers of fire control stations in their networks. Depending on where

475-580: The observations was taken from the battery itself and another from the distant station. Survey marker Survey markers , also called survey marks , survey monuments , or geodetic marks , are objects placed to mark key survey points on the Earth's surface. They are used in geodetic and land surveying . A benchmark is a type of survey marker that indicates elevation ( vertical position ). Horizontal position markers used for triangulation are also known as triangulation stations . Benchmarking

500-404: The precise or the estimated coordinates. Precise coordinates are called "adjusted" and result from precise surveys. Estimated coordinates are termed "scaled" and have usually been set by locating the point on a map and reading off its latitude and longitude. Scaled coordinates can be as much as several thousand feet distant from the true positions of their marks. In the U.S., some survey markers have

525-470: The precise point over which a surveyor's plumb-bob should be dropped to assure a precise location over it. A triangulation station was often surrounded by several (usually three) reference marks (see second photo at left), each of which bore an arrow that pointed back towards the main station. These reference marks made it easier for later visitors to "recover" (or re-find) the primary ("station") mark. Reference marks also made it possible to replace (or reset)

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550-527: 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

575-435: 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 miles; 11.2 km) apart. These distances were plugged into the triangulation equations for the pair of stations involved in sighting on

600-472: 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

625-507: 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

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