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.