A tour of a Third System fortification

The large and imposing coastal fortifications of the Third System were designed to conform to long-held principles of military engineering. As such, they displayed features that could be found in the Vauban forts built across F.urope over two centuries earlier, and certain features were continued on into the 20th century when the U.S. Army built a new series of coastal defenses.

The main component was the deployment of a large battery of ordnance on the seaward side of the fortification, while also protecting the landward side from assault by enemy storming parties. As has already been discussed, the chosen material used to construct these great fortifications was masonry, either granite blocks or, more commonly, brick. The ability to deploy a significant battery of ordnance on the Seaward side of the fortification was made possible by the emplacement of the guns and their carriages in casemates - lines of gun emplacements built from masonry and protected by bombproof roofs. In most cases, casemates were left exposed on the inner face, the one facing the central parade of the fort. These were usually stacked one on top of the other creating multiple tiers of two or sometimes three casemates. The curtain wall of the fort behind these casemates was pierced with rows of embrasures, each permitting a limited traverse for the gun located behind it. This was the key to the defensive principle of these Third System forts. Each seaward-facing side of the fort presented an overwhelming number of guns in the direction of the expected threat. Although the ability of these guns to train left or right was restricted, the sheer number of guns meant that many pieces could bear on a target at any one time. The polygonal design of the fort ensured that for the most part each side of the fortification would have a clear field of fire to its front, and out to each side at an angle of 30° to the front of the structure. The angles forming the apex of these sides (known as the salient) were not always the same, as different fort designs led to different configurations of curtains, salients and other features. Ideally, the angle was shallow enough to allow the guns on each side of the salient to provide some degree of covering fire to each other, thereby preventing

Deadzone Fortifications

In this general view of Hampton Roads and the mouth of the James River, the dominating position of Fort Monroe in the foreground is clearly evident. Connected to the mainland ofVirginia's Peninsula by a small neck of land and a causeway, the fortress acted as a vital bastion for the Union Army within a week's march of Richmond. (Stratford Archive)

Deadzone Fortifications

In this view of the outer works of Fort Monroe, an enormous I S-inch Rodman smoothbore is sited to cover the beach on the eastern side of the fort. (Stratford Archive)

a dead zone extending outwards from the salient. In practical terms, this was nearly impossible, and the front salient of most forts of the Third System remained vulnerable in this area. On top of the casemates a flat open area known as the terreplein served as a bombproof covering to the casemates below it. In most forts, an additional battery of guns was mounted on this terreplein, protected from direct enemy fire by a parapet. As these guns were often fired over the top of the parapet rather than through an embrasure, these pieces usually had less restricted fields of fire than the casemate guns below them. This meant that guns could be sited to help cover the dead zone created by the angle of the salient.

In some of the earliest Third System forts built in the United States, the salient was protected by a projecting bastion, a flanking structure that extended beyond the curtain (or scarp). While this provided extra protection for the vulnerable corner of the fort, its primary purpose was to allow defenders to fire along the line of the outer scarp of the fort using small arms of artillery loaded with grapeshot. 1'his made any attempt to scale the walls of the fort virtually suicidal.

Attackers were presented with a range of obstacles, designed to hinder their approach to the fort, and in some cases to protect its walls. Although the physical layout of forts varied, some were surrounded by sea, swamp or moat,

Fort Sumter Layout

In this view of the outer works of Fort Monroe, an enormous I S-inch Rodman smoothbore is sited to cover the beach on the eastern side of the fort. (Stratford Archive)

Fort Monroe was relatively isolated for the first year of the war and had to be re-supplied by sea. Note how the casemate guns of a water battery co the right of the picture are positioned to cover the landing stage. (Stratford Archive)

Best Fortifications

Fort Sumter

Fort Sumter, built to protect the port of Charleston, South Carolina is best known for the role it played at the start of the Civil War, where its small Union garrison was bombarded for two days.This view of the fort immediately before the outbreak of the war shows the imposing nature of the structure, and demonstrates its vulnerability to plunging mortar fire from batteries ranged around the harbor. During the Confederate bombardment the barrack buildings were destroyed, and the guns on the terreplein were put out of action. In Confederate hands Fort Sumter continued to help in the defense of Charleston, despite being reduced to rubble by Union guns.

1 Bombproof traverses

2 Officers' dining rooms

3 Fort commander's private quarters

4 Officers' quarters

5 North west stairwell

6 Northern scarp

7 Sharpshooter's platform

8 Smoothbore columbiad on wooden garrison carriage

9 Lower casemate tier 10 Upper casemate tier I I North east scarp

12 Flagpole

13 Hot-shot furnace

14 Columbiad smoothbore on en barbette carriage

15 Unmounted ordnance

16 Central stairwell tower

17 The salient

18 Rodman smoothbore on iron casemate carriage

19 Terreplein

20 Belfry

21 Grit boxes

22 South east scarp

23 Cookhouse store

24 Internal stairway

25 Enlisted mens' dining hall

26 Enlisted mens' barrack rooms

27 Offices

28 Southern scarp

29 Magazine

30 South-western stairwell

31 Gorge wall

32 Offices

33 Officer's quarters

34 Stone-built jetty

35 Sally port

Fort Macon Battery

A view from the north east corner of the terreplein of Fort Macon after her surrender in March 1862. The majority of the damage to the terreplein battery and the parade came from mortar fire, while the west scarp of the fort was subjected to the direct fire of the besiegers' rifled guns. (Stratford Archive)

Fortification Scarp

the same basic layout of outer works was used wherever the terrain permitted. The following description outlines the basic structure and the principles applied to its design and use.

First, an earthen glacis sloped up from ground level. This usually led to a brick-built wall, known as a "revetment." In theory, defenders armed with small arms could shelter behind this revetment and fire on troops advancing towards them. Behind the revetment was a strip known as the "covered way," which, rather confusingly, neither led anywhere nor was covered. Its purpose was to allow defenders holding the outer revetment of the fort to move around the perimeter of the fortification in order to react to an anticipated attack. Clearly, if the fort itself was polygonal in shape, the glacis, revetment and covered way would be constructed to reflect the angles of the fort, and any of its projecting bastions. For example, if the fort formed a hexagon, five salients or angles, in the outer defenses rather like the shape of a star, would mirror the angles of the fort. This also allowed defenders in these salients (known as "salient places of arms") to fire into the flank of attackers storming the front of the works. Smaller salients were sometimes constructed in the center of the outer defenses, midway between the main salient places of arms. On the side of the fort where the main entranceway (or "sally port") to the fort was located this small salient was larger than usual, and was known as the "re-entering place of arms." A gap in the revetment and glacis provided the main means of access in and out of the fortification.

Behind the covered way was the ditch or moat. These could be wet (water-filled) or dry. On the inner side of the moat was the main wall of the fort (known as the "scarp"), and on the inner side was the "counterscarp," a brick revetment at the inner edge of the covered way. In some cases this basic design varied due to local conditions. At F'ort Jefferson, on the Dry Tortugas, the covered way and counterscarp became a low narrow ledge separating the moat from the sea or beach beyond it. In this case, its function was more to break the force of waves crashing against the fort than to serve any defensive purpose. At Fort Jackson, below New Orleans, the moat was water-filled, and the outer works were a narrow zigzag strip of land between this formal moat and the irregularly shaped flooded ditch that lay outside the works. In effect, this acted as a second moat. Not every fort enjoyed the protection of outer works and a moat, but the efforts made to construct these features in the two examples mentioned above underline the importance the Bernard Board placed on these outlying defensive works. In some forts with dry moats, the counterscarp contained a small fortified gallery running along its length, hidden beneath the covered way itself. This brick-built structure was pierced with loopholes. If it looked as if an attacking force was about to capture the covered way, the defenders could descend into the moat and blockade themselves in the counterscarp galleries. While small arms and grapeshot from the main structure of the fort would sweep the dry moat, defenders hidden in the counterscarp galleries (also known as "counter fire rooms") could fire into the backs of the storming parties as they attempted to scale the scarp of the fort. In Fort Monroe in Virginia, parts of the covered way were replaced by a single tier of casemates (known as the water battery), while a small walkway ran along the back of them, which linked the casemates to the rest of the outer works.

On the side of the fort where the sally port was located, a drawbridge spanned the moat, linking the fort to the outer works. Usually this structure was a simple wooden affair, and could be destroyed by the defender if the outer works were captured. Sometimes a "ravelin" was built in the moat to serve as an additional form of protection for the sally port. This was essentially a triangular-shaped detached bastion, linked to both the fort and the covered way by drawbridges, l.ike the larger bastions of the main fort, this outer work was topped by a parapet, making it a small fort in its own right. This was a feature that was commonly found in forts of the Vauban era such as the Castillo de San Marcos in St. Augustine, Florida, but these works were relatively uncommon in most Third System fortifications.

Beyond the moat was the main structure of the fort itself. The casemates formed the scarp, or main brick-built outer wall of the fort. Obviously this was pierced by rows of embrasures or gunports, often protected by steel shutters that could be dropped into place to protect the guns behind them. The casemates behind formed a series of arched galleries, which were usually left exposed to the rear. In some cases, simple wooden screens were constructed on the rear face of these casemates to protect the guns and crews from the weather. Although the number of casemate tiers varied from one to three (one or two being the most common), the roof of each casemate was designed to carry both the weight of any ordnance placed on it, and to protect the casemates beneath it. A series of brick barrel-vaulted arches divided each gun bay, and provided internal protection in case part of the casemate was hit by an exploding mortar bomb or shell. While in most cases a series of arches ran at right angles to the line of the scarp, additional arches on the rear face of the casemate acted as further support for the roof above. Each arch of the vaulting was designed to distribute the immense weight of the floors equally between the outer walls and the columns at the rear of the casemate. On all casemate tiers, the floor was covered in flagstones.

Barbette Gun Carrage
A solitary medium smoothbore gun (probably a 36-pounder) mounted on an en barbette carriage remains in place after the scarp protecting the casemates and the rampart and superior slope covering the terreplein of Fort Pulaski were demolished by Union rifled guns. (Stratford Archive)
Barbette Fortification

Fort Pulaski. Georgia, sketched immediately after its surrender in April 1862.The damage inflicted by the rifled guns was concentrated on the seaward salient, at the apex of the two main casemate walls. The solitary en barbette gun on the skyline marks the point of aim for the Union gunners. (Stratford Archive)

Fort Pulaski. Georgia, sketched immediately after its surrender in April 1862.The damage inflicted by the rifled guns was concentrated on the seaward salient, at the apex of the two main casemate walls. The solitary en barbette gun on the skyline marks the point of aim for the Union gunners. (Stratford Archive)

A flat roof known as the terreplein (which was roughly equivalent to the battlements or ramparts of a medieval castle) topped the rear of the upper casemate. This stone-flagged area was protected from the direct fire of any attacker by a brick parapet, while in front of it a sloping earth-filled rampart (known as the "superior slope") provided solid protection for the gunners and soldiers on the teneplein. Compared to the casemates beneath, the terreplein was a small area, approximately half the size of the casemates, as the rampart took up the rest of the area. The rampart itself acted as a glacis, and was usually angled, falling away slightly for a few feet, then dropping sharply to meet the outer face of the scarp. The join between the rampart and the scarp was known as the "cordon," and was often reinforced by a top course of masonry that also served to prevent water damage to the casemates and scarp. Often a small step at the base of the parapet allowed marksmen to fire, as the height of the structure was usually too high to permit a soldier to level his rifle, due to the need to protect the gunners on the terreplein.

On some forts, an additional curtain wall (known as a "detached scarp," or "Carnot's wall") rose up from the top of the scarp, acting as an additional barrier. The top of this brick-built structure was usually a little lower than the top of the earthen rampart behind it, and was separated from the superior slope by a narrow walkway (known as the "chemin de ronde"). The detached scarp was usually loopholed for use by marksmen, while a passageway or gallery underneath the rampart provided access to the interior of the fort. This feature was incorporated into the defenses of Fort Clinch on Amelia Island, Florida, a pentagonal fortification built between 1847 and 1861.

T he center of a fort was occupied by a large open space known as the "parade." While this was used as a drill ground, it was also often used to house barrack blocks, storehouses, a shot-heating furnace, water cisterns, magazines and other structures, as well as a flagpole. Occasionally, forts omitted a conventional parade ground, and the central area was filled with soil or sand to improve the protection afforded to the casemates. In these cases, the fill of the parade area sloped down towards the rear of the fort, where a series of offices, stores and buildings abutted the landward scarp. The Advanced Redoubt built to augment the defenses of Pensacola, Florida, between 1845 and 1859 was constructed along these lines. While this solution offered the best protection against mortar bombs, more conventional System Three forts were left vulnerable to indirect fire from explosive shells or bombs lobbed over the walls into the parade. Consequently in time of war, a series of pits was often dug in the parade to contain the blast from these shells, and earthen banks were raised to protect the rear faces of the magazine and the casemates. Freestanding buildings in the interior of the fort were built along conventional mid-19th-century lines, and usually consisted of long two- or three-storied buildings topped with gabled tile roofs. The magazine building was usually well protected by a surrounding blast wall, or in some cases (as in Fort Moultrie, South Carolina), the structure was built in a slot cut in one of the protective bastions. In the event of a direct hit on the magazine, the stout walls of the building were designed to stay in place, encouraged by extensive buttress work. This directed the blast upwards through the roof, therefore limiting the damage to the rest of the fort. At least that was the theory. In practice, forts

Fort Moultrie

Fort Moultrie was a small coastal fortification, built on Sullivan's Island to protect Charleston, South Carolina. Several versions of the fort were built on the same site, but by the outbreak of the Civil War the walls of the Third System fortification were cracked, and sand blocked its line of fire over the harbor. After its capture by South Carolina militia, repairs were made, the sand was moved, and the guns in the fort participated in the bombardment of Fort Sumter. Fort Moultrie remained in Confederate hands until the fall of Charleston in February 1865. In this view the South Carolina State flag is shown flying over the fort.

Fort Jefferson Hot Shot Furnace

under attack by indirect fire such as lort Jackson and Fort St. Philip on the Mississippi River distributed their powder and shot around the casemates, where it was thought they would be better protected. In forts with bastions, small ready-use magazines were housed in these structures, as was the case in Fort Jefferson on the Dry Tortugas. Naturally, the lower levels of the bastions housed guns designed to fire along the line of the moat covering the approaches to the scarp.

In some forts the barrack rooms and officers' quarters were located on the landward face of the fort, a structure sometimes called a "redan." This was often pierced by the sally port, which split the redan into two equal parts. Forts built in this manner include Fort Sumter, South Carolina; l ort Schuyler, New York; Fort Pulaski, Georgia; Fort Zachary Taylor, Florida, and Fort Carroll, Maryland. In a number of other forts, buildings were concentrated inside a central citadel, which served as a final line of defense. Built like a medieval keep, these square or round stnictures contained a lower floor of storerooms and kitchens, while upper floors contained barrack rooms, officers' quarters and offices. Like the Martello Towers found in smaller fortified sites, these structures could be topped by a parapet and fighting position or by a tiled roof.

While the rear defenses of most forts varied greatly, the latest military thinking of the 1840s called for a distinction to be made between the moat on the seaward and flanking sides of the fort, and the moat on the landward side. In the Advanced Redoubt at Pensacola, the two areas were separated by additional structures; low passageways that ran across the moat and connected the inner and outer works. This structure was known as a "caponnier," combining the function of a covered passageway with that of a defensive position. The idea was that soldiers retiring from the outer defenses could enter the capponiers, then fire through loopholes in either side when enemy troops reached the moat. Some were simply a pair of open-topped parapets, but most took the form of brick-built passageways above ground. These structures divided the landward area of the moat from the other sides. In these cases, the moat on the landward side was referred to as a "gorge."

Any assault on a well-fortified and fully manned Third System fortification would have been a prohibitively costly operation. Although the structures varied from location to location, the general principles of defense remained the same. The only flaw in the whole design was that by 1861, attackers no longer needed to launch costly attacks on these fortifications. Advances in weapons technology meant that in most cases, they could simply be shelled into submission.

Coastal Fortifications

In this view of the interior of Fort Pulaski after the siege of April 1862, a 10-inch mortar lies half-buried by debris on the terreplein of the south-east face of the fort. In the background the smoothbore gun pointing skyward marks the salient of the two faces of the seaward side of the fort. This was the point where the Union gunners concentrated their fire. (Stratford Archive)

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