coast defense

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Fire Control Structure Details

The photo gallery at left illustrates a number of details of Boston fire control structures (FCSs) that were found while exploring the harbor defenses.

Slide 1 shows the ceiling of one of the observation levels of the Marblehead-South fire control tower, with a few well-preserved details. The telephone line conection box at right connected the tower to the harbor communications system. Lines ran from there to the 3-wire connection points on the ceiling, from which lines dropped down to the headsets worn by the observers positioned on this level. The time interval bell was probably mounted on the grey wall panel at center, and was also connected by communications wire. The windows are original, and had wooden shutters.

Slides 2 and 4 (also from Marblehead) show, respectively, a steel mounting column for an azimuth telescope (used to scan the ocean and track ships) and the concrete mounting pad for a larger depression position finder (DPF) instrument, with its three nuts and bolts intact. The steel column is the only one the author has found in the harbor defenses. These mounting columns and pads often had their centers surveyed to register the precise locations of the instruments mounted on them.

Slide 3 shows an azimuth telescope (M1910) used by the Coast Artillery in WW2. These scopes could be mounted on steel columns (like that in Slide 2) or on tripods as shown here. This scope was served by a crew of two: one man to observe and another to read the resulting azimuths off the scale (on the left side of the instrument) and phone these in to the plotting room or gun battery. The wiring on the scope was for lighting its reticle and dials, and was connected to a power source via a large matching coil (not shown here) that supplied constant voltage to the scope. [This scope is on display (in 2010) at the museum of the Halibut State Park fire control tower in Rockport, MA.]

Slide 5 shows a very rare surviving placard from the Marblehead-South tower which lists the so-called datum points used for adjusting the DPF on one of its observation levels (base end station No. 4 for Btty 206, the six-inch guns at East Point in Nahant). The instrument would be focused on the listed landmark and the azimuth and range-to-target indicated by the DPF would be compared with the pre-measured values listed here (which had been surveyed by the Army Engineers). This had to be done frequently, since the DPF was very sensitive to variations in the height-of-tide and could go out of adjustment for various reasons. [After racking my brain to identify a stone tower in Revere, MA I plotted out the bearing and found that the datum point in fact referred to the tower atop Telegraph Hill at Fort Revere, in Hull, MA.]

Slide 6 shows the only surviving Boston example (again from the Marblehead-South tower) of "faux" tower construction detail, designed to camouflage the exterior of a fire control tower. Slide 7, also from the same tower, shows the only surviving coal stove in the Boston system. This stove, on the 1st floor of the tower, must have allowed heat to rise and heat the upper levels, which also had their own flue connections and perhaps their own stoves.

Slide 8 shows a survey marker, used to locate a tower's observing instruments, which was set in the roof of the Pt. Allerton tall tower. Today, seeing one of these marks is unusual, because markers like this have often been covered by re-roofing or tar, or are inaccessible because the tower's roof hatch has been sealed shut. While we're in Pt. Allerton, Slide 9 shows what has got to be the best view in the Boston Harbor defense system, from the top of this 8-story tower.

Slide 10 illustrates a Battery Commander's station at Btty Ward, Ft. Strong, Long Island, part of the Endicott Period defenses of the harbor. This photo is included here to provide an example of a type of structure that is not counted on this website as a fire control structure (FCS). During the period 1900-1920, the observation station atop this concrete tower (note the armored door hanging open at its rear) was likely used as one end of a baseline for controlling the fire of Btty Ward (which mounted older 10-inch guns on disappearing carriages), or as an emergency DPF position for the Battery Commander. But by WW2 almost all of these older gun batteries had been scrapped from the harbor defenses, so their fire control positions went with them.

Therefore, older stations of this type, which were almost all located in the Harbor Island forts) were not given location or site numbers in the WW2 coast defense system. Also, these older stations generally did not receive survey markers, indicating that they were not included in the survey program of the Army Engineers (which began in the late 1930s) that layed out the WW2 fire control network.

Selected Details

  • Tower-Interior
    This is the interior of one of the two observation levels in the Marblehead-South fire control tower, Location 132-1A. The tower is adjacent to a residence. (PG 2010)
  • AZ-Scope-Mounting-Pillar
    The most prevalent observing instrument used in the fire control system was the M1910 Azimuth Telescope. Some of these were located on top of precisely surveyed mounting pillars like the one shown here. Others were supported by simple tripods, like that shown in Slide 3 . Tripod-mounted scopes might be placed next to one of the larger depression position finder (DPF) instruments and used to track targets or spot the fall of fire. (PG 2010)
  • M1910-Azinuth-Scope
    This telescope was designed specially for use by the Coast Artillery. It had a side-mounted crank to turn it smoothly in tracking a target. The wires shown here ran to lights that illuminated dials or the telescope's viewfinder. (PG 2010)
  • DPF-Base
    This octagonal concrete pad was used to mount a depression position finder (DPF), a telescope that could measure range as well as azimuth from its location to the target. The center of such a pad, found by connecting its vertices and marking the intersection of the resulting lines, was often a precisely surveyed position. It was sometimes located directly beneath another survey marker embedded in a building's roof (see Slide 8). (PG 2010)
  • Datum-Pts-Mbhd-South
    This placard, from the Marblehead-South fire control tower, lists the azimuths and ranges of a variety of points, called datum points, that were used to check the caibration of the instrument. These telescopes were hyper-sensitive, and needed to be adjusted multiple times during a day. (PG 2010)
  • Marblehead-South-Faux-Windows
    Peering through the ivy vines on the seaward side of the Marblehead-South fire control tower reveals the faux widow details that were added to the exterior as camouflage. Only the narrow vision slits are functional windows. The 4-over-3 "paned" window sash details are only tacked on to the concrete walls of the tower. One wonders what difference this was thought to make in "camouflaging" this 5-story tower, which stuck out well above the rooflines of its neighboring houses. (PG 2010)
  • Surviving-Stove
    This small coal stove, with its sheet metal stack piping, is original to the Marblehead-South fire control tower. The other items around it are "stuff" stored in the tower by its nearby homeowner. This tower is also one of the very few that features a basement. (PG 2010)
  • Roof-Top-Disk
    The brass disk in the rooftop of the tall fire control tower at Pt. Allerton in Hull marks the centers of the observing instruments on its lower levels, which are located precisely one above another. The latitude and longitude of this mark is recorded in the database of the National Geodetic Survey. The railing around the edge of the tower is a modern addition to this privately-owned tower. (PG 2010)
  • Harbor-From-Allerton
    This photo looks northwesterly from atop the 8-story Pt. Allerton fire control tower in Hull, MA. The Boston skyline is at left. The Logan Airport control tower is at center. The tall hump of an island just to the right of downtown is the summit of Ft. Strong on Long Island, with Ft. Warren on Georges Island in front of that (the corner of one of the fort's granite casemates is clearly visible). In the distance at right center are the sewage digester "eggs" of the new MWRA plant on Deer Island, former location of Ft. Dawes. Ft. Standish on Lovells Island lies in from of that, behind the line of barges being towed out to sea. At the far right, the red, white and blue water tank in Winthrop can just be discerned against the horizon. This photo clearly shows the commanding view from this tower across all approaches to Boston Harbor. (PG 2010)
  • Battery-Commander's-Station
    This photo looks westerly at the Battery Commander's station for Btty Ward, an Endicott Period battery of 10-inch guns at Ft. Strong. The raised concrete enclosure was needed to elevate the station over the parapet in front of the guns, which were mounted on disappearing carriages. Stations like this are not counted in this website's tally of fire control structures. (PG 2010)