Robert E. Lee, as a newly commissioned West Point graduate, was assigned for two years to Cockspur Island, where he was involved in the early stages of draining and building up the site in preparation for constructing the fort. The fort itself is a Third System work (fortifications authorized by the U.S. Congress beginning in 1818). The Third System differed from earlier coastal fortification programs in being conceived as an integrated system to deny enemies maritime access to American waterways rather than defending individual ports. Fort Pulaski adhered to the concept of vertical forts embraced by the U.S. Army Corps of Engineers; such fortifications provided concentrated firepower against ships via multiple levels of cannon housed in masonry casemates. Although masonry walls were vulnerable to sustained cannon fire, the relatively small naval cannon mounted on constantly rocking ships minimized this threat.
Like its sibling, Fort Sumter (begun 1828) in Charleston Harbor, Fort Pulaski was designed for two levels of casemates, but the unstable marshy ground resulted in a single level of casemates with a second level of cannon on the terre plein above. Beneath the foundation, the soft ground was stabilized with a network of timber pilings, while the weight of the fort was dispersed through reverse arches and battered walls in the foundation. Within the casemates, a clear distinction can be seen between the local Savannah Grey brick employed for the piers and the stronger imported brick employed for the complex groin vaulting. The fort displays a level of masterful craftsmanship in its brick masonry that is matched by few buildings in the Savannah area.
The fort was designed primarily by Joseph G. Totten, head of the army’s Fortifications Board and later chief engineer of the corps. It features Totten casemates, designed together with special fore-pintle gun carriages to provide a wide arc of fire through unusually small embrasures, originally protected by self-opening iron shutters. The thirty-degree arc of fire from centerline resulted in the truncated hexagonal shape of the fort, since the cannon mounted in adjacent waterside faces could turn at maximum traverse to provide continuous coverage. Vents in the casemate vaults assisted with clearing smoke from the cannon. The back side or gorge of the fort includes an elaborate sally port with drawbridges over the moat. Demibastions in the gorge flanks are equipped with special flank howitzers to rake the gorge wall with canister shot in the event of attack.
The National Park Service interpretation of Fort Pulaski is focused on its Civil War history and the rapid reduction of the fort by land-based, rifled cannon on April 10, 1862 (the first significant use of rifled artillery in combat, which heralded the end of masonry vertical fortifications). The eastern faces of the fort retain the damage from the 1862 bombardment, with multiple projectiles still embedded in the walls.