Siege artillery in the American Civil War

Siege artillery is heavy artillery primarily used in military attacks on fortified places. 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. "Field artillery" were light pieces that often traveled with the armies. "Siege and garrison artillery" were heavy pieces that could be used either in attacking or defending fortified places. "Seacoast artillery" were the heaviest pieces and were intended to be used in permanent fortifications along the seaboard. They were primarily designed to fire on attacking warships Harv |Gibbon|1863| p=54. The distinctions are somewhat arbitrary, as field, siege and garrison, and seacoast artillery were all used in various attacks and defenses of fortifications. This article will focus on the use of heavy artillery in the attack of fortified places during the American Civil War.

The weight and size of siege artillery prevented it from regularly travelling with the armies. When needed, siege artillery and other material needed for siege operations were assembled into what was called a siege train and transported to the army. In the American Civil War, the siege train was always transported to the area of the siege by water.

The siege trains of the Civil War consisted almost exclusively of guns and mortars. 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.

Pre-war siege artillery

Prior to the war, the U.S. Army had a variety of iron smoothbore siege guns (12-, 18-, and 24-pounders) and howitzers (24-pounder and 8-inch) Harv |Gibbon|1863| pp=54–9. None of these pieces were used during the war as siege artillery. The advent of rifled artillery made them obsolete.

The Federal siege train

Rifled guns

The Civil War was the first major war to see the use of rifled artillery. Rifling gave the guns greater velocity, range, accuracy and penetrating power, making smoothbore siege guns obsolete. The ranges of these guns is somewhat problematic. The 6.4 inch (100-pounder) Parrott rifle had a maximum range of 8,845 yards (5 miles) Harv |Parrott|1863| p=5. However, the absence of suitable sights Harv |Abbot|1867| pp=89-90. and a good system of directing fire on targets that could not be seen from the gun, limited the effective range of the rifled guns.

The bombardment of Fort Pulaski demonstrated that rifled guns were extremely effective against masonry fortifications. 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.

James rifles

During the early part of the war, the Federal army lacked rifled siege artillery. 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. However they were retired from frontline service soon after.

Smoothbore guns Rifled with James System

Wooden mortars

The Union Army of the Tennessee, not having a proper siege train at the siege of Vicksburg, was forced to improvise. The artillerymen took short sections of gum-tree logs, bored them out to accept six or twelve pound shells, and hooped the logs with iron bands. These wooden mortars reportedly served well Harv|Hickenlooper|1888| p=540. Edward Porter Alexander reported that Confederate experiments with wooden mortars were not successful Harv|Alexander|1883| p=110.

Mortar gallery

Confederate siege train

The Confederate Army had no siege train "per se", as they did not engage in regular sieges. 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.

The Confederate equivalents to the heavy Parrott rifles were the Brooke rifles. They were cast iron guns with wrought iron breech bands like the Parrott rifles. They generally had a bore of 6.4 or 7 inches, and had single, double, and even triple bands.

During the siege of Petersburg the Confederate Army developed iron 12-pounder and 24-pounder Coehorn mortars. The rough iron pieces served very well.

Use of siege artillery during the American Civil War

Bombardment of Fort Pulaski

U.S. Army command decided to block Savannah, Georgia's access to the Atlantic Ocean by capturing Fort Pulaski downstream from Savannah on the Savannah River. Federal forces made an unopposed landing on Tybee Island December 24, 1861. Guns and supplies for the reduction of Fort Pulaski were landed on Tybee Island on February 21. The siege batteries were ready by April 9. Fort Pulaski was then armed with 48 guns, 20 of which bore on the batteries on Tybee Island- 14 smoothbore guns and columbiads, 1 24-pounder Blakely rifle, and 4 mortars. The garrison was 385 men.

At sunrise April 10, 1862, the Federal forces formally demanded the surrender of Fort Pulaski, the demand was refused and at 8:15 AM the first shot was fired. Confederate return fire was vigorous, but not very accurate and Fort Pulaski was breached that afternoon. The James rifles and 4.2-inch Parrott rifles did most of the damage to the fort. The Federal mortar fire was very inaccurate. After nightfall, a desultory fire was kept up, to prevent the Confederates from repairing the breach. After sunrise on April 11, firing resumed, and the breach was rapidly enlarged and eleven Confederate guns dismounted or otherwise rendered unserviceable. At 2:00 PM, Fort Pulaski surrendered. Remarkably, only one man on each side was killed in the lengthy artillery engagement.

The fall of Fort Pulaski demonstrated that masonry fortifications were obsolete in the era of rifled artillery. General Gilmore, senior Federal engineer officer at Fort Pulaski, quoted a military treatise of the period as saying an “exposed wall may be breached with certainty at distances from 500 to 700 yards … and it will take from four to seven days firing ….” Harv |Gilmore|1882| p=161. That had been with smoothbore guns, with rifled guns firing at distances of over 1,600 yards, the breach had been made in a day and a half.

Federal siege batteries at Fort Pulaski

Bombardment of the city of Charleston

Gilmore determined to bombard the city of Charleston. Under the existing rules of warfare, Charleston was a legitimate target. It was fortified. It contained weapons factories, and it was a port for blockade runners who carried contraband of war. But more importantly, Charleston was the symbol of rebellion. It was there that South Carolina became the first state to secede. The firing on Fort Sumter in 1861, which started the war, only increased the North’s belief that Charleston’s destruction seemed just retribution. Harv |Wise|1994| p=169.

Using tremendous skills and ingenuity, Gilmore's engineers constructed the "Marsh Battery" in the marsh between James Island and Morris Island. 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. At a range of 7,900 yards, the gun was aimed by taking compass bearings off [http://www.stmichaelschurch.net/02c_history.php St. Michael’s church’s] steeple. The first night, 10 incendiary and 6 explosive shells were fired into the city. The gun was not fired on the 23rd. On August 24, firing its 36th round the Swamp Angel burst. In its short life the Swamp Angel made artillery history it was the longest ranged artillery bombardment and it was the first time artillery had been aimed by compass bearing Harv |Wise|1994| p=172. The Swamp Angel was not replaced in the Marsh Battery, but after the fall of Fort Wagner and Fort Gregg Federal batteries located in and near Fort Gregg (renamed Fort Putnam) resumed fire on the city of Charleston, continuing until the city was evacuated. .

iege of Petersburg

During the siege of Petersburg, no attempts were made by Federal artillery to level the Confederate works. Attempts to clear the abatis in font of the works by gunfire were unsuccessful. 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. Rifled guns in Federal batteries on the James River were used against the Confederate James River Flotilla Harv |Abbot|1867| p=85.

With rifled guns unable to harm opposing forces behind earthen field works, mortars became more important. Federal forces fired over 40,000 mortar rounds during the siege, and the Confederates returned a nearly equal fire Harv |Abbot|1867| pp=18–9.

The Federal forces successfully mounted a 13-inch seacoast mortar on a railroad flatcar. This mortar was nicknamed the “Dicatator.” The car was moved along a section of the Petersburg and City Point Railroad to bring different points along the Confederate lines under fire. When charged with 14 pounds of powder the mortar would recoil less than two feet on the flatcar, but the flatcar would recoil 10 to 12 feet on the tracks. The plane of fire had to be nearly parallel to the tracks, to allow the flatcar to recoil and avoid dismounting the mortar, but by using a curved section of track a wide traverse could be achieved. Fire from the “Dictator” was very effective. At a range of 3,600 yards, one round was reported as having blown a Confederate field gun and carriage above the parapet of the Confederate works Harv |Abbot|1867| p=23.

Federal Siege Train at the Siege of Petersburg"April 2, 1865"Source: Harv|Abbot|1867| p=160

Notes: The 8-inch siege howitzer is not reported to have been fired Harv|Abbot|1867|pp=169–70.

The presence of the Confederate 4.6-inch Brooke rifle in the Federal siege train is unexplained. It was emplaced in Fort Cummings and could presumably have fired ammunition designed for the 4.5-inch siege rifle. It is also confusingly reported as being of English manufacture Harv|Hunt|1894| p=660.

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External links

* [http://civilwarfortifications.com/index.html Civil War Field Fortifications Web Site]
* [http://www.civilwarartillery.com Civil War Artillery Projectiles]