The Performance of Coast Artillery Guns
The table below lists the ranges of the principal guns of the Coast Artillery that defended Boston Harbor between 1898 and 1946. [NOTE]
| Ranges of Boston Guns and Mortars | ||
| Gun/Mortar | Yards | Miles |
| 16-inch Army M1919 on BC | 49,100 | 27.8 |
| 16-inch (Navy Mk II M1) on BC | 44,680 | 25.4 |
| 12-inch M1895 A2 on BC | 29,300 | 16.6 |
| 12-inch M1888 on DC | 15,134 | 8.6 |
| 12-inch M1895 on DC | 11,636 | 6.6 |
| 12-inch mortar (M1890) | 14,610 | 8.3 |
| 10-inch M1900 on DC | 14,162 | 8.0 |
| 10-inch M1888 M1 on DC | 12.259 | 7.0 |
| 6-inch (M1) on BC | 26,250 | 14.9 |
| 6-inch (M1900) on BC | 14,400 | 8.2 |
| 3-inch (M1903) | 11,000 | 6.3 |
| 90mm (M1) | 8,000 | 4.5 |
In Boston, for example, harbor defense in the Endicott-Taft Period (1895-1915) was provided principally by 10-inch and 12-inch rifles on disappearing carriages (DC) in the harbor forts, supported by many batteries of 3-inch rapid fire (RF) guns. As the table shows, this gave the harbor defenses an outer reach of some 7 to 8 miles. If we take average range as 7.5 miles, this would be roughly the distance between Battery Stevenson at Fort Warren (the 12-inch guns on Georges Island) northerly to East Point in Nahant or southeasterly to the coast in Hingham just below the base of the Hull peninsula. This would mean that the guns on Georges Island could engage enemy ships positioned roughly 12 miles from the State House in downtown Boston.
The table also underlines the importance of 12-inch mortar batteries during this early period. They exceeded all but the 12-inch M1888 (DC) in range, and possessed wide fields of fire (360 degrees, although most were not expected to be employed in this manner). [NOTE]
In the 1920s, Boston's defenses were up-gunned, with the addition of the 12-inch barbette carriage (BC) guns of Btty Gardner in Nahant. These guns had almost three times the range of the 12-inch DC guns emplaced only 10-15 years earlier. The 16-inch guns of Btty Long on Hog Island were also added during the 1920s, using the Navy guns displaced by naval treaties between the wars, This extended the range of Boston's armament to 25 miles.
Then, as WW2 dawned, the older DC guns and the mortar batteries were scrapped (after a life of only some 25 years), and the defenses were augmented by newer (M1) 6-inch batteries that offered almost twice the range of their earlier (M1900) counterparts and by 90mm guns for rapid fire, close-in defense. Selected batteries of older 3-inch guns were retained throughout WW2.