Civil War Field Fortifications

Sea Coast Fortifications

All  permanent fortifications occupied by Confederate forces and attacked by Federal forces during the Civil War were Third System (built after the War of 1812) sea coast fortifications. Almost all of these fortifications deviated from the archetypical standards for permanent fortifications in more or less substantial ways that deserve closer examination. Perhaps the most striking deviation was the use of hollow casemated masonry walls rather than solid earthen ramparts to enclose the fortified space. This design characteristic was influenced by the objective of sea coast fortifications: they were primarily intended to serve as platforms for large batteries to prevent enemy fleets from passing through narrow channels leading into important inland waterways and commercially significant harbors. While a solid earthen rampart only allowed one tier of guns mounted on the terre-plein, a hollow casemated wall allowed two or three tiers of guns, more than doubling the volume and weight of fire that could be brought to bear against an enemy fleet attempting to run the channel or engage the fort to silence its guns. Casemated walls also allowed greater overall design flexibility and spatial economy since the compartments could interchangeably serve as battery positions, garrison spaces, magazines, and bomb-proof shelters. Where an earthen rampart had to have a relatively wide base with wide slopes to support its own weight, a masonry wall could be built on a relatively narrow foundation that greatly economized interior space and reduced the overall length of walls needed to enclosed the fortified space.  Arched masonry casemate walls were also relatively more difficult to breach than masonry revetted earthen ramparts due to the greater thickness of the masonry and its much greater resistance to both solid shot and shell.

American sea coast fortifications in general varied from the archetypical standards for permanent fortifications quite substantially in the use of outworks. Some fortifications received very strong outworks designed to enhance the garrison's ability to resist an attack by regular siege approaches, some received a bear minimum of protection for their scarp walls while others were given no protection at all. The landside defenses of Fort Adams, which guarded Narragansett Bay, Rhode Island included a strong crown work with scarp walls protected by tenailles; forts Morgan and Macon relied on heavy built up glacis to cover the scarp wall. Fort Pulaski, on Cockspur Island in the Savannah River received absolutely no protection for its scarp walls. Vulnerability to an attack by regular siege approaches was the primary determining condition for inclusion of outworks. Though positioned at the tip of a peninsula, the landside of Fort Adams was easily accessible and open to an attack by regular approaches. Fort Morgan was positioned at the tip of a long and very narrow peninsula that offered few advantages for an approach. The fort  itself was considered sufficiently large to control the ground immediately exterior to the glacis without extensive outworks. It was also assumed that its guns would be able to prevent an enemy fleet from passing into Mobile Bay and that naval forces inside the bay would be able to cooperate with the fort against an attempt to attack the place by regular approaches. The site of Fort Pulaski was chosen in part because it was well beyond effective heavy smoothbore artillery breaching range of any solid ground where batteries might be established while Cockspur Island's marshy soil was considered impractical for an attack by regular approaches. The fort was only thought to be vulnerable to infantry assault by escalade and was therefore only provided with a low earthen demilune (or ravelin) which did not cover the scarp wall form distant artillery fire. The glacis, like the ravelin, did not provide any protection for the scarp walls and was only built up high enough to bring its crest into the line of fire of the fort's main casemated  armament.

Most of the sea coast fortifications held by the Confederates were designed to take advantage of the curtain and bastion system of reciprocal defense, but there were some important exceptions. The design of Fort Macon, one of the oldest of the Third System forts, was given an irregular pentagonal outline without bastions and re-entering angles. Its ditch was defended by loop holes  and small embrasures in the scarp walls along with short counterscarp galleries that provided flanking fire.  Fort Macon was a very small fort and part of its main armament was positioned on terre-plein of the covered way, quite an unusual arrangement. Two of the four salient angles of the scarp wall were rounded off, another unusual and flawed feature, which was mitigated by the fact that the fort's main armament was mounted en barbette and did not depend on exacting angles to produce strong columns of fire. Barbette mounting also allowed artillery on the terre-plein to cover the sectors without. The fort's casemates were neither designed nor prepared to mount the fort's main armament, but could mount field pieces when necessary. Although the glacis was built up to cover the body of the scarp wall, the masonry parapet was exposed to distant artillery fire.

Arrangements for reciprocal defense at Fort Pulaski were reduced to a minimum primarily because the fort was thought to be practically invulnerable to close attack by land forces. Flanking arrangements for the pentagonal shaped fort were limited to extensions of the scarp walls that overlapped and flanked the gorge. These extensions, which are often referred to as demi-bastions (half bastions), were casemated and provided with embrasures that allowed flanking fire down the faces of the demilune and across the gorge wall. Embrasures facing the gorge were designed to limit the reach of their light howitzer armament to prevent them from firing into the opposite extension. Garrison spaces within the gorge wall were loop-holed for small arms fire, but were not equipped with embrasures. The salient angles of the scarp wall were truncated to form pan coupes that all but eliminated sectors without fire and allowed the fort's main casemated armament to defend the crest of the glacis with direct fire.

Fort Jackson at Plaquamine Bend on the Mississippi River south of New Orleans was given a regular pentagonal shape with bastions covering the slaient angles. The fort was protected from attack by two wet ditches which were separated by a narrow glacis that covered the land faces of the fort from distant artillery fire. The north bastion and its adjoining curtains fronting the Mississippi were not covered by the glacis. Perhaps the most interesting and unusual feature of Fort  Jackson was its combination of solid with casemated walls. Only the two faces fronting the Mississippi River were casemated and capable of receiving the fort's main armament. The south curtain was filled solid while the other two contained chambers to defend the sally port and the fort's magazine. While central citadel was prepared for defense with crenelated walls, it was too lightly constructed to withstand artillery fire, particularly vertical fire delivered by mortars. When Fort Jackson was subjected to a heavy and prolonged mortar bombardment prior to the passage of the Federal fleet the citadel was wrecked and burned.

These examples show that the design of permanent fortifications, like that of field fortifications, was not simply a matter of drawing pretty and symetrical pictures that included as many of the various fortification elements as possible. Each fortification had to be designed to suit its site, its objective, and it had to account for the strength of the most probable type of enemy attack that the fortification would be compelled to withstand.  When these forts were designed and constructed rifled artillery did not exist and their designers only accounted for the penetrative effects and breaching ranges of heavy smoothbore artillery. The reduction of Fort Pulaski, followed closely by the siege of Fort Macon, showed that masonry fortifications could not resist the effects of rifled artillery; both forts were surrendered after  intense bombardments and well before the attacking forces were prepared to assault the fortifications. It must also be pointed out that sea coast fortifications relied on the participation of naval forces to be able to conduct their strongest defense. The Confederate Navy was incapable of providing and sustaining the support necessary to the successful defense of any of the fortifications bombarded, besieged, and surrendered to Federal land forces.

Permanent Fortifications

Contents    Home Page    Major Works    Minor Works    Siege Works    Glossary

Copyright (c) PEMcDuffie 1998