When built in the antebellum period, Fort Sumter could stand against the most likely threat to itself and Charleston harbor – wooden sailing vessels standing to bombard the fort. But by the fall of 1863, the fort had fallen once to bombardment from land batteries (in April 1861), and was at that time being pounded into rubble by another bombardment. Although this latest bombardment was the heaviest, up to that time, in American history, simple demolition of the walls and reduction of its armament would not neutralize the fort’s importance as a link in the defensive chain protecting Charleston. The threat of sharpshooters and light cannon fire from Fort Sumter could deter any attempt by the U.S. Navy to clear the obstacles at the harbor entrance.
As Federal cannons destroyed more of the fort’s original structure, the likelihood of another direct assault by boat. To counter that threat, Confederate defenders improved the existing defenses to include features and weapons not contemplated when Fort Sumter was built. For example on the night of November 7-8, 1863, engineers recorded the following work done:
Force, 170 hands; discharged 2,700 bags of sand and some timber; repaired, raised, and enlarged traverse over west circular stairway; filled mortar holes on gorge bomb-proof and traverse in rear of northeast lower casemate battery. Carpenters worked on ladders, ventilators, and chevaux-de-frise; being obliged to remodel the latter. No wire fencing yet built, as the expected posts and frames have not yet arrived from the city.
I would point out that some of those “hands” were slaves requisitioned by the Confederates for such work.
In the Civil War context we normally consider chevaux-de-frise as an obstacle designed to stop cavalry:
But the threat to Fort Sumter was not the mounted arm. Rather from marines, sailors and soldiers scaling up the rubble from boats. The Federal bombardment would turn these into splinters in short order. The Confederates needed something light enough to put out at night (or other times when landings were expected) and have a low profile to avoid damage. Photos taken at war’s end show some of those modified chevaux-de-frise:
Notice the orientation of the “barbs” on these chevaux-de-frise. Laying on a frame, the points would impede those scaling up the rubble. At the base of the wall, to the left, are some of the posts for wire fencing mentioned in the report.
Another postwar view of the fort shows the modified chevaux-de-frise from above:
And this view also brings up two of several very light artillery pieces used by the Confederates as anti-landing weapons. As the Confederates removed the heavy guns from the fort, these light field pieces came in to provide close range fire to cover potential landing points around the fort. In this case 12-pdr mountain howitzers. At night, these were wheeled out of hiding and placed appropriately around the fort’s battered parapet. At daybreak they were moved back under cover for protection. But that didn’t always ensure the howitzers were safe. On November 8, Colonel Alfred Rhett wrote in the singular sense about “the” mountain howitzer employed in the fort, and damage to the weapon:
The mountain howitzer, though placed in a position of supposed security, was struck in the chase by a fragment of a mortar shell, causing a convexity in the bore. This, I think, can be removed by boring out. The piece was sent up per steamer Randolph last night and contains a round of case shot.
Notice the howitzer was loaded with case shot while employed in this role. If I may again dig at my favorite target of late… not canister! For preventing boat landings, case shot could reach out a bit further than canister and stop the enemy before touching ground. I’m reminded of Rear-Admiral Dahlgren’s original experiments with boat howitzers and the use of case shot, prior to the war, in that regard.
Chevaux-de-frise, mountain howitzers, and other defensive measures transformed Fort Sumter from a seacoast artillery platform into a secure observation post and sharpshooter’s nest. Arguably the transformation was a success, as the post would not fall to direct assault during the war.
(Citations from OR, Series I, Volume 28, Part I, Serial 46, pages 635-6.)