Union troops at Vicksburg were so desperate for siege weapons they made logs into mortars.
During the early phases of the Vicksburg Campaign, General Ulysses S. Grant tried using both direct assault and maneuver to dislodge Confederate forces from the high banks along the Mississippi River. When those assaults failed on May 22, 1863, the Union commander turned to siege operations. Facing a shortage of critically needed mortars to implement his strategy, his engineers turned to do-it-yourself alternatives. Lieutenant Peter C. Hains wrote of using “spring boards” to launch 6-pounder shells into Confederate works. Even more useful were wooden mortars produced on the spot, reportedly made “by shrinking iron bands on cylinders of tough wood, and boring them out for 6 or 12 pound shells.” The cylinders, in this case, were the trunks of large trees. Those ersatz mortars were credited with 100- to 150-yard ranges during the battle.
Transitioning a field army to siege operations was a complex process, involving more than just a simple siege declaration. A besieging army would usually find tools such as spades, picks and axes much more valuable than muskets. After all, though combatants were often within smoothbore range of each other, earthwork defenses and terrain made them relatively immune from direct, line-of-sight fire.
Because field guns, which fired projectiles on a limited trajectory, were useful only to batter fortification walls, the besiegers also relied on high-trajectory howitzers and mortars to lob shells over works and into the enemy’s trenches. When Grant began the Vicksburg siege, however, his army possessed only one large 10-inch mortar, too heavy to maneuver into the trenches.
To deal with such contingencies, the U.S. Army had authorized the use of lightweight mortars in the field, a policy long predating the Civil War. The concept actually dated back to the 17th century, when Dutch engineer Baron Menno van Coehoorn introduced a series of light mortars for siege operations. Americans were already familiar with the British 12-pounder (41⁄2-inch) “Coehorn” and the 24-pounder (51⁄2- inch) “Royal” because they had been used during 18th-century wars. In 1838 the U.S. Army standardized the design of a 24-pounder Coehorn.
In 1861 barely 30 Model 1838 Coehorns existed, but by the spring of 1863 48 additional guns had been constructed. The Union Army had sent the weapons on hand to the Eastern armies and fortifications in threatened sectors, including the Washington, D.C., defenses, leaving Vicksburg’s hard-pressed besiegers to their own devices.
Teams of engineers, infantrymen and other artillerymen all used the improvised wooden mortars during the 47-day siege. Their tactics included covering batteries, sap rollers and approach trenches. To reduce a defensive fortification, a besieger built a base trench line with lunettes for artillery batteries. Surveying the defenses, the attacker selected an approach that took advantage of blind angles in the enemy works. Next the besieging force built advancing trenches in a zigzag pattern out from the base trench. The lines of the zigzag never exposed a flank, or straight, shot to enemy guns. While digging the trenches, the troops used sap rollers or other similar protection. After closing the range, the besieger placed mortars in the zigzag, usually holding their fire until a final assault on the works.
On July 1, the Federals exploded a mine directly under a redan occupied by the 6th Missouri (Confederate) to breach the Confederate lines. In the aftermath, Federal troops opened fire with a mix of heavy smoothbores, rifled guns, field howitzers and a 12-pounder wooden mortar. Colonel Francis Cockrell of the 1st Missouri Brigade reported, “This mortar did us great damage, having exact range of our position and throwing shells heavily charged with powder.” Cockrell’s superior, Maj. Gen. John Bowen, said, “they fire shell with heavy bursting charges, and our men are killed and wounded with fearful rapidity.” Another Confederate division commander, Maj. Gen. John Forney, complained of “what is supposed to be a Cohorn mortar, which throws its missiles among the men with great accuracy, killing and wounding many, and tending much to dishearten the men.”
The rough-hewn mortars clearly made an impression upon the Confederates as well as the victorious Federals. A year later at Petersburg, both armies had ample quantities of real Coehorn mortars on hand, ready for more siege operations.
Craig Swain, from Leesburg, Va., is a self-confessed cannon fanatic who maintains the blog “To the Sound of the Guns.”
Originally published in the June 2012 issue of Civil War Times. To subscribe, click here.
