American coastal defenses were modernized from the 1890s to 1910 with the developement of the Endicott System. Emphasis in military tactics shifted the masonry forticications to more effective weapons based on rifled steel guns, improved breech-loading systems, better propellants (gunpowder), and reinforced concrete gun emplacements.
Here you will see the remains of Bettery Decatur, a reinforced concrete emplacement completed in 1891. It mounted two 10-inch dissapearing guns similar to the Fort Monroe rifled gun shown in the photographs below. The lower rooms of the battery were for shot, shell, and powder storage with cranes and hoists that moved the heavy ammunition up to the gun platforms.
Ingenious disappearing carriages used recoil energy to lower the gun out of sight of the enemy for reloading and servicing. These 10-inch guns had a firing range of approximately seven miles.
The guns were aimed and fired by means of complex range finding and fore control equipment centered in the Battery Commander's Station, visable to your left. This Depression Position Finder, mounted in the tower, located the target exactly.
Fort Washington Park
Source: U.S. Department of the Interior, National Park Service