Siege artillery in the American Civil War

At the time of the American Civil War, the U.S. Army classified its artillery into three types, depending on the gun's weight and intended use.

The distinctions are somewhat arbitrary, as field, siege and garrison, and seacoast artillery were all used in various attacks and defenses of fortifications.

Guns fired projectiles on horizontal trajectory and could batter heavy construction with solid shot or shell at long or short range, destroy fort parapets, and dismount cannon.

Mortars fired shells in a high arcing trajectory to reach targets behind obstructions, destroying construction and personnel.

Prior to the war, the U.S. Army had a variety of iron smoothbore siege guns (12-pounders, 18-pounders and 24-pounders) and howitzers (24-pounder and 8-inch) (Gibbon 1863, pp. 54–59).

60–61) While guns were intended to batter down the walls of a fortification during a siege, mortars were designed to fire explosive shells over the walls of the fortification, killing the men inside, and forcing others to stay in bombproof shelters, or preventing the gunners from serving their guns and repairing damage caused by the bombardment.

Mortars could also destroy structures inside the fortification such as barracks and kitchens which would normally stay unharmed from standard guns.

58–59) Lastly, these could also kill men where other guns couldn't reach them The 8-inch and 10-inch siege mortars had maximum ranges of 2,225 and 2,064 yards, respectively, (Abbot 1867, pp.

Later experiences at the campaign against Charleston Harbor and the siege of Petersburg showed that rifled guns are much less effective against earthen field works.

To fill this gap, the army rifled existing smoothbore pieces with the system developed by Charles T. James.

Firing shot and shells also designed by James, these newly rifled smoothbores gave good service during the bombardment of Fort Pulaski in April 1862.

(Dew, p. 187) The 6.4-inch (100-pounder) Parrott Rifle was a potent siege gun capable of great accuracy and long range with heavy projectiles.

General Quincy A. Gilmore, commander of the Federal forces at Charleston, said "[t]here is, perhaps, no better system of rifled cannon than Parrotts; certainly none more simple in construction, more easily understood, or that can with more safety be placed in the hands of inexperienced men for use."

One 10-inch Parrott rifle on Morris Island was disabled soon after it first opened fire by the premature detonation of a shell, which blew about 18 inches off its muzzle.

The ragged end of the muzzle was trimmed even by soldiers working with cold chisels, and the gun fired another 370 times without any appreciable difference in range or accuracy.

The Federal forces at Charleston used two British 5-inch Whitworth muzzle-loading rifles that had been captured aboard a blockade runner.

Shells failed to take the rifling, exploded prematurely, and solid shot could not reach their target (Wise 1994, p. 157).

In defending the works that were the objects of Federal siege operations, the Confederates used a hodge-podge of weapons seized from Federal arsenals and fortifications, naval guns, Confederate-made versions of pre-war designs, and imported rifled guns, such as the Whitworth and Armstrong rifles.

After sunrise on April 11, firing resumed, and the breach was rapidly enlarged and eleven Confederate guns dismounted or otherwise rendered unserviceable.

Morris Island was occupied, Fort Sumter was reduced, and the presence of Federal batteries sweeping the main channel into the harbor, effectively closed Charleston as a port for blockade runners.

However, the long struggle on Morris Island gave the Confederates time to strengthen the harbor's other defensive works, and the U.S. Navy did not enter Charleston Harbor until after General William T. Sherman's advance through South Carolina finally forced the Confederates to evacuate the city on February 17, 1865.

Work on most of the batteries for the pieces that were to bombard Fort Sumter was completed by August 16, 1863, and firing began the next day.

All of the parapet gun were dismounted or seriously damaged and the fort was no longer an effective part of the defenses of Charleston Harbor (Turner 1890, p. 216).

The Atlantic Ocean flank of the second parallel was anchored by "Surf Battery" built below the high tide line.

A Federal officer inspecting the fort after its occupation said "Notwithstanding the heavy fire of this bombardment, together with all the fire Fort Wagner had been subjected to since the commencement of our attack, from land and naval batteries, its defenses were not materially injured; that is to say, the parapets, bomb-proofs, and traverses of sand still remained and would have afforded shelter to infantry behind them, though greatly tossed about and torn up by our projectiles, but, under our fire, it was impossible to serve their artillery, nor could they expose themselves outside of their bomb-proof for an instant" (Turner 1890, pp. 218–219).

The firing on Fort Sumter in 1861, which started the war, only increased the North's belief that Charleston's destruction was just retribution.

An 8-inch Parrott Rifle, nicknamed the "Swamp Angel," was mounted in the battery, and began firing at the city at 1:30 AM, August 22, 1863.

The rifled guns were therefore used to keep down the Confederate fire, annoy their working parties, interfere with traffic on the Petersburg bridges, and to repel or support assaults.

With rifled guns unable to harm opposing forces behind earthen field works, mortars became more important.

The Dictator silenced the Confederate guns on Chesterfield Heights to prevent them from enfilading the right end of the Union line.