In our zeal to examine Gettysburg, we often overlook the other major Federal victory in July 1863. As both armies at Gettysburg reeled from three days of bitter fighting, on July 4 the Confederate defenders of Vicksburg, Mississippi surrendered, marking the end of a protracted campaign aimed at opening a section of the Mississippi River. During the early phases of the campaign, General U.S. Grant attempted by both direct assault and maneuver to dislodge Confederate forces from the high banks along the Mississippi River at Vicksburg. Only after assaults on May 22 failed did combat evolve into siege operations.
The transition of a field army, organized and equipped for open maneuver, to siege operations is a bit more complex than simply declaring a siege. Items which a field army have limited use for – particularly spades, picks, and axes – are more valuable than muskets when constructing approaches within the siege lines. Within the artillery batteries, field guns, although useful for some battering of enemy walls, had less impact than on the open fields of battle. Instead, howitzers and mortars, which could lob shells over the works and into the enemy trenches, were much more valuable.
As the besiegers’ parallel lines advanced closer toward the defender’s lines, mortars in particular were extremely useful. Even though combatants were often within smoothbore musket range of each other, the earthwork defenses and terrain (if the defender did his job right) prevented direct line of sight fires. However the mortar’s high angle trajectory could drop explosive shells inside the enemy works, covering those digging the approach trenches.
But Grant’s army had only one mortar on May 22 – a large 10-inch mortar which was too heavy to maneuver into trenches. Pre-war, the Army authorized light mortars for use with field armies to meet just such contingencies. The concept actually dated back well before the American Revolution. The Dutch-Sweedish engineer Baron Menno van Coehoorn introduced a series of lightweight mortars for siege operations during the 17th century. American were familiar with the British 12-pdr (4 1/2-inch) “Coehorn” and 24-pdr (5 1/2-inch) “Royal” from use during the 18th century wars. In 1838, the U.S. Army standardized the design of a 24-pdr “Coehorn.” 
However doctrine, military necessity, and funding seldom intersect during peacetime. While authorized in 1838, production of the 24-pdr mortar was slow. Barely thirty Model 1838 Coehorns existed at the outbreak of war. Early war production remained limited, with only 48 additional examples produced by the time of the Siege of Vicksburg. Those that were produced were issued to the eastern armies and fortifications in threatened sectors, notably the Washington defenses.
Faced with this shortage of needed weapons, the engineers at Vicksburg turned to alternatives. Lieutenant Peter C. Hains wrote of “spring boards” to launch 6-pdr shells into the Confederate works. But more useful were wooden mortars produced during the siege. These were produced “by shrinking iron bands on cylinders of tough wood, and boring them out for 6 or 12 pound shells.” Presumably the cylinders were the trunks of large trees. The ersatz mortars were credited with 100 to 150 yard ranges.
Crude as it was, the mortars made quite an impression upon the defending Confederates. On July 1, Federals exploded a mine directly under a redan occupied by the 6th Missouri (Confederate), with the purpose of exposing a breach in the Confederate lines. In the aftermath, Federals opened fire with a mix of heavy smoothbores, rifled guns, field howitzers, and a 12-pdr 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, Major General John Bowen (division commander), further added with regard to the mortar, “they fire shell with heavy bursting charges, and our men are killed and wounded with fearful rapidity.”  Another Confederate division commander, Major General John Forney, complained at the same time 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.” 
Perhaps the impression was amplified by the grind of the siege. However the Confederate commanders appeared to understand what impact these light mortars in the trenches could have on their defenses. The Federals employed the wooden mortars as part of a team composed of engineers, infantry, and other artillery, with tactics including mines, sap rollers, and approach trenches.
The story of the gun here – a weapon does not need to be backed up with a pile of patents or some sophisticated production method in order to have an impact upon the battlefield (as was the case with the 3-inch Ordnance Rifle of yesterday’s post). In the trenches at Vicksburg, a weapon without such high pedigree was rather effective.
Happy Independence Day to my readers on this July 4th, also the anniversary of the surrender of Vicksburg.
- Birkhimer, William Edward, Historical Sketch of the Organization, Administration, Materiel, and Tactics of the Artillery, United States Army, (Washington: J.J. Chapman, 1884) p. 275.
- Ibid. p. 282.
- Olmstead, Edwin, Wayne E. Stark, and Spencer C. Tucker, The Big Guns: Civil War Siege, Seacoast and Naval Cannon (Alexandria Bay, NY: Museum Restoration Service, 1997), Appendix D 137, pp. 335-7.
- Report of Lieutenant Peter C. Hains, U.S. Army Corps of Engineers, Chief Engineer, Thirteenth Army Corps, dated July 30, 1863, Official Records, Series I, Volume 24, Part II, Serial 37, p. 186.
- Reports of Captains Frederick E. Prime and Cyrus B. Comstock, U.S. Army Corps of Engineers, Chief Engineers Army of the Tennessee, dated November 29, 1863, Official Records, Series I, Volume 24, Part II, Serial 37, p. 173.
- Report of Col. Francis M. Cockrell, Second Missouri Infantry, commanding First Brigade, dated August 1, 1863, Official Records, Series I, Volume 24, Part II, Serial 37, p. 416.
- Reports of Brig. Gen. John S. Bowen, C.S. Army, commanding Division, dispatch dated July 2, 1863, Official Records, Series I, Volume 24, Part II, Serial 37, p. 413.
- Reports of Maj. Gen. John H. Forney, C.S. Army, commanding Division, dispatch dated July 2, 1863, Official Records, Series I, Volume 24, Part II, Serial 37, p. 363.