Siege artillery is heavy artillery primarily used in military attacks on fortified positions. 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 . 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-pounders, 18-pounders and 24-pounders) and howitzers (24-pounder and 8-inch) . None of these pieces were used during the war as siege artillery. The advent of rifled artillery made them obsolete.
Federal siege train
Mortars
Three primary types of mortars were used during the war: siege & garrison (light), seacoast (heavy) and Coehorns are also classified as siege & garrison. 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. Heavier mortar shells could penetrate magazines and many bombproof shelters.
In defense of fortifications, siege and garrison mortars could harass work parties constructing siege batteries and trenches. Their fire could also suppress hostile siege batteries. Seacoast mortars could penetrate the decks of wooden ships and even threaten the deck plating of ironclad vessels. 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, and the 13-inch seacoast mortar had a maximum range of 4,300 yards, but their effective ranges were much shorter. For the 8-inch siege mortar at a range of 800 yards, about 50% of the shells would fall within a 50-yard radius of the target. With the 10-inch siege mortars at 875 yards, about 60% of the shells would fall within a 40-yard radius of the target. The 13-inch seacoast mortar could be expected to be more accurate.
Coehorn mortars were lighter mortars, designed to be brought well forward in the trenches.
With the replacement of masonry fortifications with earthen works, mortars became more important. Works that could resist the horizontal fire of guns were still vulnerable to the vertical fire of mortars.
Name Weight of shell Weight of mortar weight of bed Coehorn mortar M. 1841 (5.82-inch) 17 lb. 164 lb. 132 lb. 8-inch siege mortar M.1841 44 lb. 930 lb. 920 lb. 10-inch siege mortar M. 1841 88 lb. 1,852 lb. 1,830 lb. 10-inch seacoast mortar M. 1841 88 lb. 5,775 lb. --- 13-inch seacoast mortar M. 1861 197 lb. 17,120 lb. ---
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 . Edward Porter Alexander reported that Confederate experiments with wooden mortars were not successful .
Mortar gallery
Rifled artillery
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 . However, the absence of suitable sights 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. The reduction of Fort Macon two weeks later confirmed this. 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.
4.5-inch siege rifle
The 4.5-inch siege rifle looks like a larger version of the 3-inch ordnance rifle and it is often called a 4.5-inch ordnance rifle. However, the 4.5-inch siege rifle was of conventional cast iron construction and did not use the welded wrought iron construction of the 3-inch ordnance rifle. The 4.5-inch siege rifle fired shells weighing about 30 pounds (depending on the specific type of shell). The tube weighed 3,450 pounds and was 133 inches long. The gun's only vice was that it suffered from excessive erosion of the vent caused by the hot gasses flowing through the vent when the gun was fired. The vent could become too large to fire the piece after 400 discharges. This problem could be remedied by insertion of a copper vent piece (bouche).
In addition to its use as siege artillery, two batteries of 4.5-inch siege rifles (8 guns total) accompanied the Army of the Potomac as "heavy" field artillery between 1862 and 1864. The big guns were intended for long range firing against Confederate artillery. Although the guns showed very good mobility, they saw little action.
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 artillery rifled with the James system
Name Bore Weight of projectile Weight of gun Length of gun 24-pdr M. 1839, rifled (48-pdr James rifle) 5.82 in. 48 lb. (shot) 5,790 lb.124 in. 32-pdr M. 1829, rifled (64-pdr James rifle) 6.4 in. 64 lb. (shot) 7,531 lb. 125 in. 42-pdr M. 1841 rifle (84-pdr James rifle) 7 in. 64 lb. (shell)
(shot) 8,465 lb. 129 in.
Parrott rifles
Robert Parker Parrott (1804–77), an 1824 graduate of the United States Military Academy, developed a new form of rifled artillery using a cast iron barrel with a reinforcing wrought iron band around the breech. He first produced 2.9-inch (10-pounder) and 3.67-inch (20-pounder) rifles for the field artillery. He later produced four larger rifled guns that were used as siege artillery. These heavy Parrott rifles became the mainstays of the Federal siege train.
Name Weight of projectile Weight of gun Length of gun Range 4.2 inch Parrott rifle (30-pdr Parrott rifle) 25 lb. (shell) 4,200 lb. 132 in. 6,700 yd. @ 25° 6.4-inch Parrott rifle (100-pdr Parrott rifle) 90 lb. (shell) 9,700 lb. 155 in.8,845 yd. @ 35° 8-inch Parrott rifle (200-pdr Parrott rifle) 150 lb. (shell) 16,500 lb. 162 in. 8000 yd. @35° 10-inch Parrott rifle (300-pdr Parott rifle) 250 lb. (shell) 26,500 lb. 177 in. ---
4.2-inch (30-pounder) Parrott rifle
The 4.2-inch (30-pounder) rifles were the most widely used of the Parrott siege guns. The tubes were mounted on a conventional siege carriage. The early pattern guns had the elevating screw under the breech, while the newer pattern gun had a long screw running through the cascabel. The long elevating screws of the newer models were prone to breakage . The 4.2-inch Parrott rifles were preferred over the 4.5-inch siege rifles because of the superiority of Parrott shells over the various shells available for the 4.5-inch siege rifle. The 4.2-inch Parrott rifles did not have as great a propensity for bursting as found in the larger Parrott rifles. During the siege of Petersburg 44 4.2-inch Parrott rifles fired 12,209 rounds , but only one gun burst when a shell detonated before clearing the muzzle . One 4.2-inch Parrott rifle also burst during the campaign against Charleston harbor, but only after it had fired 4,606 rounds .
Two new examples of a Confederate-made variant of a 30-pounder Parrott were also employed in defensive positions at the Battle of Fredericksburg. Both pieces burst in action there, one on the 39th and the other on the 54th discharge. (Dew, p. 187)
6.4-inch (100-pounder) Parrott rifle
The 6.4-inch (100-pounder) Parrott Rifle was a potent siege gun capable of great accuracy and long range with heavy projectiles. For siege use it was mounted on a front pintle barbette carriage. It did, however, tend to burst. Of the three hundred 6.4-inch Parrott rifles in service with the U.S. Navy, 19 burst . During the campaign against Charleston harbor, one burst at 122 rounds and another burst at 1,151 rounds . The army retained their enthusiasm for the guns. 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." . A 100-pounder was also fired from Fort DeRussy during the Battle of Fort Stevens in Washington, DC.
8-inch (200-pounder) Parrott rifle
The 8-inch (200-pounder) Parrott Rifle was essentially an enlarged 6.4-inch Parrott rifle with the same vices and virtues. The most famous 8-inch Parrott rifle was the "Swamp Angel" used for the bombardment of the city of Charleston. It burst on its 36th discharge.
10-inch (300-pounder) Parrott rifle
Only three 10-inch (300-pounder) Parrotts saw service during the war; all placed on Morris Island during the campaign against Charleston harbor. It was mounted on a center pintle, barbette carriage. It was essentially an enlarged 8-inch Parrott rifle, although it was believed to be somewhat more accurate than the 8-inch rifle . 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 gun was subsequently permanently disabled by additional premature detonation of shells.
Parrott rifle gallery
Whitworth rifle