Civil War Era Mortars
While guns were intended to batter down the walls of a fortification, mortars were designed to fire explosive shells over the walls of the fortification, killing the garrison, forcing the garrison to stay in bombproof shelters, preventing the garrison from serving their guns and repairing damage caused by the bombardment. Mortars could also destroy structures inside the fortification such as barracks and kitchens. Heavier mortar shells could penetrate magazines and many bombproof shelters.
Using a small powder charge, a mortar can throw large, hollow projectiles at high elevations, unlike other artillery pieces of the Civil War. For practical purposes the mortar is a smoothbore weapon.
The 12 lb. and 24 lb. Coehorn Mortars
The Coehorn mortar, a small muzzle-loading mortar, caliber generally 5.82 inches, is named for it's Dutch inventor, Barron Menno van Coehorn (1641-1704). Mounted on a block or platform, it was portable, easily adjusted, took little powder, and was particularly effective in sieges. The US Army had a 24-pounder brass Coehorn that weighed 164 pounds, or 296 pounds when mounted on it's four-handled oak mortar bed. Two men could move this mortar, but four men could better maneuver and rush this mortar into position in unprepared locations. Explosive shells could be lobbed into masked targets from 50 to 1,200 yards with the Coehorn.
Although the Model 1841 24 pdr. Coehorn is the most widely used on the Union side, the Confederate army did cast and use Iron 12 pdr. Coehorns, with a bore of 4.62 inches, as well as Iron 24 pdrs. As the war progressed, trench warefare became quite common, and mortars were found to be increasingly useful.
- Type: 24 pdr. Model 1841 Coehorn Mortar
- Rarity: Common
- Years of Manufacture: 1841 - 1865
- Tube Composition: Bronze
- Bore Diameter: 5.82 inches
- Standard Powder Charge: 1/2 lbs.
- Projectiles: 16.8 lbs. Round Mortar Shells
- Tube Length: 16.3 inches
- Tube Weight: 164 lbs.
- Overall Weight: 296 lbs.
- Range (at 45°): 1,200 yards
- Invented By: Dutch inventor, Baron van Menno Coehoorn
- Special Notes: Photo at right is cropped from a larger photo from the Library of Congress: Broadway Landing, Va. Federal ordnance at the depot, 1865.
The 8 and 10 inch Mortars
Larger siege and seacoast mortars are sometimes incorrectly referred to as Coehorns. At the time of the Civil War, three sizes of siege and seacoast mortars were common and considered standard: the 8-inch, the 10-inch, and the 13-inch mortar. 8-inch and 10-inch siege mortars had a maximum ranges of 2,225 and 2,064 yards, respectively, but their effective ranges were much shorter. For the 8-inch siege mortar (image left) 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 Siege & Seacoast Mortar
The 13-inch seacoast mortar had a maximum range of 4,300 yards. The 13-inch seacoast mortar could be expected to be more accurate than it's smaller counterparts.
- Type: Model 1861 13 inch Siege & Seacoast Mortar
- Rarity: Uncommon
- Years of Manufacture: Between 1860 and 1864
- Tube Composition: Iron
- Bore Diameter: 13 inches
- Standard Powder Charge: 20 lbs.
- Projectiles: 200 lbs. Round Mortar Shells
- Tube Length: 56.5 inches
- Tube Weight: 17,250 lbs.
- Range (at 45°): 4,325 yards
- US Casting Foundry: Fort Pitt Foundry, Pittsburgh PA
- Special Notes: The mortar photographed at right is located in Ringwood State Park in NJ, Registry No. 27, Fort Pitt, 1861, and is noted for participating in the Seige of Vicksburg.
The 13" Union Seacoast Mortar saw action in many different theaters in the American Civil War. It was used by both the Army and the Navy. The official records site that four 13-inch mortars participated in the capture of Island No. 10. General Gillmore had a dozen, which took part in the reduction of Fort Pulaski, which protected Savannah. There were 20 mounted on schooners, which participated in the action against Fort Jackson and Fort Saint Philip below New Orleans. A 13-inch mortar was used to shell Fort Pillow and during the Yazoo Pass expedition a navy scow carried one which was used to shell Fort Pemberton. This mortar was also very popular with Grant. He used them in both naval and land based batteries during the siege of Vicksburg. McClellan placed seven 13-inch mortars in Battery #4 at Yorktown. General Gillmore also used these guns to reduce Battery Wagner and Fort Sumter.
One of the most famous guns of the war was the well photographed "Dictator" which fired 200 pound mortar shells from a railroad platform propelled by 20 pounds of powder into the Confederate lines during the siege of Petersburg.
Finally, there are the makeshift wooden mortars of the era. Confederate 12-pdr. mortars made of wood were used at Petersburg, and Union forces imployed 6 and 12-pdr. wooden mortars at Vicksburg when Coehorns were in short supply. These mortars were made from logs of the toughest wood, were bored out, and were bound with strong iron bands. Less accurate than their bronze and iron counterparts, these mortars proved more successful for Union artillerists at shelling large Confederate held towns than Confederate attemps to shell small Union Army positions in the field.
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