These six batteries conform to the three-part defense system of the Endicott plan: large-caliber batteries (Garland, Fenwick, Brumby) directed fire against ships; a mortar battery (Habersham) provided plunging fire against ships; and small-caliber, rapid-fire batteries (Backus, Gantt) defended an electrically controlled minefield beneath the shipping channel from smaller vessels.
Battery Garland (1899), now the Tybee Island Museum, mounted a single 12-inch gun with a range of eight miles. The network of spaces within the museum once included separate magazines for powder charges and projectiles, serviced by a system of overhead tracks and hoists for raising and transferring ammunition to the gun platform above. The latter is accessible on the roof level, but the loading platform has been filled with concrete. A stairway provides access to the wide concrete blast apron, now used as a viewing platform, which prevented muzzle blast from excavating the earthen berm in front of the battery. Battery Fenwick (1899), a near duplicate of Battery Garland, is now a private residence and cannot be viewed from public grounds.
Battery Brumby (1898) mounted four 8-inch guns on disappearing carriages. It is partly restored and partly accessible to the public, although the left gun emplacement is now a private residence and the right is the Tybee Island Shrine Club. Magazines and service rooms on the lower level are open to the rear and were secured by heavy wooden doors during operations, with additional iron gates that allowed the doors to remain open for ventilation. The gun platform above includes several early innovations. The working platform, the circular pit where the gun was mounted, now has cast-in steps to the surrounding loading platform. The wider loading platform provides access to the magazine hoists on the left with an added concrete bridge on the right for emergency access to hoists of the adjacent gun. There are two magazine hoists: the earlier balanced platform hoist with two access doors employed a pair of elevators that shared a central pulley system, while the more refined Taylor-Raymond Hoist used a continuous chain drive system. The concrete splinter shield above the hoists was an additional improvement.
Battery Backus (1900) was unusual in being designed to mount a single American-made 6-inch gun and two British 4.7-inch Armstrong guns. The 6-inch-gun platform is visible on the right. This small caliber battery did not employ magazine hoists, as the fixed ammunition (projectile and gunpowder combined in a shell) was hand-carried from the lower magazine up to the gun platform. The gun platform on the left side has partly collapsed due to the removal of the earthen berm.
Battery Gantt (1900) is artfully preserved as the foundation level of the residence on piers above. This battery mounted two 3-inch rapid-fire guns and is nearly identical to Battery Hambright at Fort Pulaski (15.4.4). It also employed fixed ammunition with no magazine hoists.
Battery Habersham (1900), which is privately owned but can be effectively viewed from the outside, represents the final refinement of the Endicott mortar battery, a passing concept in the development of American coastal artillery. The mortar battery directed plunging fire from a high trajectory into the poorly protected decks of early armored warships. The inherent inaccuracy of this tactic resulted in mounting a group of mortars that fired simultaneous volleys in a gridlike pattern. Unlike earlier examples that consisted of four enclosed pits arranged in a square, each with four mortars, this battery is linear and open to the rear, with magazine access from the rear as well. Its design dispersed blast effect, greatly reducing damage from the concussion of mortar volleys. The number of mortar pits was reduced from four to two as the result of more effective firing practices.