by Gordon Thorsby
A Confederate Coehorn Mortar LOC
The canister from a Napoleon twelve-pounder smoothbore was terrifying because it could take down a dozen men in packed lines of infantry. However, during several months between June 1864 and March 1865, the falling shot from a Coehorn mortar was king and it tormented every soldier on both sides even when men were behind the deep entrenchments at Petersburg.
The effectiveness of the light artillery decreased in 1864 when the Lee’s army was forced into defensive fighting while Grant’s Federal army hammered away. Massive Union assaults proved futile and static fighting took over. Union Artillery Chief Brig. Gen. Henry Hunt had a possible solution and he called on a two-century old weapon, the Coehorn mortar. It was tested at Spotsylvania and Maj. Gen. John Gibbon, an artillery man from Academy days, was thoroughly impressed. Hunted ordered thirty.
A mortar in the Trenches, Waud
The Coehorn (misnamed Cowhorn in 1775 Boston during its siege) was the smallest of all of the mortars at Petersburg; a portable 5.82-inch gun platform that could lob an 18.6 shell from 50-1200 yards. The weapon was fixed in a 45-degree position on top of a wooden box. Accuracy was sufficient where approximately 50% of the shells fell within a 50-yard radius of a target. Like any weapon, the shorter the distance to target, the greater was its accuracy. The distance to target was addressed by the size of the charge and the mortar was fired by a standard friction primer similar to light artillery. Two or three men could move the 175-pound gun (with four handles) and fire, then displace and fire from a different spot. A seven-man crew was designed to work the gun, but it could easily fire with fewer cannoneers at a slower rate.
The bronze Union Coehorn fired round solid shot or shell. The light artillery fired during the day. The mortars owned the night with a dazzling lightshow, that is until the round shot entered a crowded redoubt or the shell exploded over manned rifle pits. The shell fragments maimed and killed while the concussion knocked others senseless. Shells that had fuses set too long often burrowed themselves into the mud and exploded with dramatic “wumpfs,” a lot of smoke and none or few casualties.
Hunt distributed the Coehorns in forward positions in the trenches by June 17, 1864 and more heavily in the IX Corps salient. V Corps Artillery Brigade commander Col. Charles Wainwright had his batteries quickly trained on the firing of the weapon behind the main lines and it was put into use with other caliber mortars. Of all of the shells fired by various Federal guns at Petersburg, the shot and shell of a Coehorn was responsible for 17%. Its use was third only to the Napoleon twelve-pound cannon and 3” Ordnance Rifle, the two most common artillery guns of the entire war.
After one week of its mortar fire, Confederate Colonel E.P. Alexander had to address the Coehorn. He ordered steel-made Coehorns of his own on June 24 but more was required because casualties mounted casualties on men, animals and guns. Literal "ducking" for the Confederate soldier was not an option.
The trenches of Petersburg (LOC)
Groups of Confederate sharpshooters advanced on Coehorn positions and fired on the mortar teams. Union Infantry and artillerymen near the mortars began to dread their own Coehorn positions because they were often the unintended sharpshooter victims. The Coehorn targets could be anything but trenching parties and gun emplacements near front lines in the dark of night were the favorites.
Eventually, the mortar was employed on both sides and just another tool that made Petersburg a miserable place. The men dug deeper and the bombproof became commonplace. The endless nature of siege warfare continued for nine-months and every soldier dreaded each day. Indirect artillery fire was the new ruler of the battlefield.
Naisawald, L. VanLoan, Grape and Canister The Story of the Field Artillery of the Army of the Potomac 1861-1865, Stackpoole Books, 1999. ISBN 0-8117-0702-4.
Hess, Earl J., Civil War Field Artillery, Promise and Performance on the Battlefield, Louisiana State University Press, 2023. ISBN 2023 978-0-8071-7800-3.