Civil War Fortifications Tour Museum of the Confederacy, April 5, 2003 The great destruction of life, in open assaults, by columns exposed within so long a range, must give additional value to entrenched fields of battle; and we may again see fieldworks play the part they did in the defense of Sebastopol; and positions so chosen and fortified that not only will the assailant be forced to entrench himself to assail the enemy, but will find the varying phases of his attack met by corresponding changes in the defensive dispositions. --Dennis Hart Mahan, West Point, 1863 Definition A military earthwork is defined as any primarily earthen structure erected for a military purpose. During the Civil War, earthworks were called intrenchments, trenches, rifle or shelter trenches, rifle pits, parallels, earthen defenses, or breastworks, or just works often interchangeably. Military earthworks were an integral part of military operations from the beginning and throughout the war. The veteran soldiers ability to rapidly construct shelter for themselves learned during 1863 and developed to a fine art in 1864 constituted a principal tactical innovation of the Civil War. Types of Construction The parapet is the protective mound of earth. The ditch is the excavation from which the dirt is removed. A fill of logs, fence rails, or stones is piled up along the intended line before digging begins. The revetment is a retaining wall of logs, planks, sandbags, or stones added to hold the earth vertical. The illustration below left shows front (exterior) ditch construction, favored by engineers for both artillery and infantry works when time permitted. The advantage is that the ditch (like a dry moat) provided an additional layer of defense; the ditch can be deeper and the parapet fatter. The example below right shows a typical rifle trench constructed rapidly in the field. The ditch was usually dug deep enough so that a standing soldier could steady his weapon atop the parapet. The advantage of rear (interior) ditch construction was speed every scoop of earth simultaneously lowered the ditch and raised the parapet. Sometimes, the soldiers would dig a rear-ditch work and later make the parapet fatter by excavating a second front ditch (often when taking incoming artillery rounds!) A captured line of earthworks could be turned, dug by the captors to face in the opposite direction. Digging In A unit deployed in formation along a line selected by the officers, typically along the military crest of a local terrain feature, and began digging with bayonets and other makeshift tools, throwing the earth toward the enemy. Working parties gathered fence rails, downed trees, or stones, and pile these materials along the line, adding bulk to the growing parapet. When available, entrenching tools shovels, picks, and axes were passed from unit to unit to deepen and improve the position. One pick loosened enough earth to keep two shovels hard at work. In the woods, axe-men cut down trees and brush in front of the line to open a clear field of fire. Within two or three hours, depending on soil type and vegetation, an entire line could be entrenched to a relief of four feet, so that the parapet would cover the chest of a soldier standing in the ditch. Page 1 of 6 MOC Earthworks Tour 1
Military Earthworks Logic The modern military uses an acronym KOCOA for analyzing the combat value of terrain and for positioning troops on the battlefield. These letters stand for Key Terrain; Observation and Field of Fire; Cover and Concealment; Obstacles; Avenues of Approach and Withdrawal. These principles applied as much in 1864 to the siting of field fortifications as today. In 1864, General Henry Hunt distilled four rules for siting artillery: 1) The efficacy of fire of the battery (observation and field of fire); 2) Cover for the pieces from the enemy's fire (cover and concealment); 3) The position of the rest of the troops (key terrain and mutual support); and 4) Facility of movement (avenues of approach and withdrawal). Official Records, Serial 88, pp. 574-575. Entrenchments enhanced the combat value of the terrain by seizing the military crest to eliminate defilade (dead ground), which provided an extended field of fire and simultaneously cover and concealment. KOCOA Classification is based on scale, time in preparation, and function. The large prepared-in-advance fortification at far left (Class 1 or 2) dwarfs the rapid exterior-ditched infantry work center and the rearditched rifle trench at right (Class 4). Obstacles such a felled-trees, palisades, or entanglements were typically placed 50-100 yards in front of the earthwork to delay and break up an attack. Federal Soldiers in their Rifle Trenches along North Anna River (detail of impromptu sun shades) Page 2 of 6 MOC Earthworks Tour 2
Earthworks Classification (Adopted by the Civil War Fortifications Study Group at Nashville, 1999) Class One: PREPARED ARTILLERY ENTRENCHMENTS Includes forts, redoubts, bastions, lunettes, redans, batteries, blockhouses Builders: laid out or renovated by engineers Type of construction: "classic" prototypes, front-ditched, revetted Materials: gabions (wicker baskets filled with soil), sandbags, fascines (long, bound bundles of saplings), log, plank, sod, stone revetments Dimensions: 12-20+ feet relief, 15-25+ feet width of parapet Features: artillery platforms, embrasures, firing-steps, additional interior works Situation: semi-permanent defense of towns, depots, transportation routes, river crossings, sieges; may be improved from rapid entrenchments during prolonged battle situation. Class Two: PREPARED INFANTRY ENTRENCHMENTS Includes siegeworks, main lines or breastworks, parallels, connecting curtains, blockhouses Builders: laid out or renovated by engineers Type of construction: typically front-ditched, revetted Materials: log, plank, sod, stone revetments Dimensions: 6-15 feet relief, 12-25 feet width of parapet Features: firing-steps, traverses, individual shelter pits Situation: semi-permanent defense of towns, depots, transportation routes, river crossings, sieges; may be improved from rapid entrenchments during prolonged battle situation. Class Three: RAPID ARTILLERY ENTRENCHMENTS Includes breastworks, minor artillery "lunettes" or demi-lunes Builders: typically laid by field officers for their units, thrown up quickly, often under fire Type of construction: front-ditched, rear-ditched, ditch-both sides, revetted or not Materials: materials at hand - piled stone, fence rail, or log fill - log, sapling, fence rail, wicker, stone revetment Dimensions: 3-6 feet relief, 12-15 feet width of parapet Features: artillery platforms, traverses, holes for ammo chests Situation: battlefield, bivouac, defense of roads, railroads, river crossings Page 3 of 6 MOC Earthworks Tour 3
Class Four: RAPID INFANTRY ENTRENCHMENTS Includes breastworks, rifle trenches Builders: typically laid out by field officers for their units, thrown up quickly, often under fire Type of construction: front-ditched, rear-ditched, ditch-both sides, revetted or not Materials: materials at hand - piled stone, fence rail, or log fill - log, sapling, fence rail, wicker, stone revetment Dimensions: 2-5 feet relief, 8-15 feet width of parapet Features: bays, balks, traverses, "command" holes Situation: battlefield, bivouac, defense of roads, railroads, river crossings Class Five: COMMUNICATION AND SUPPLY Includes communication trenches, covered ways, entrenched military roads, zigzag trenches Builders: laid out by engineers or field officers Type of construction: front-ditched, rear-ditched, ditch-both sides, parapet both sides, revetted or not Materials: earth, log, stone or wicker revetment Dimensions: ditch 3-15 feet wide Features: associated holes and bunkers for storage Situation: semi-permanent fortifications, siegeworks, or prolonged battle when front line troops need resupply Class Six: INTERNAL WORKS Includes magazines, bombproofs, bunkers, traverses associated with enclosed or semienclosed artillery fortifications Builders: laid out by engineers to strengthen prepared positions Type of construction: square or rectangular hole with surrounding berm, sometimes roofed; internal parapet designed to provide defilade Materials: earth, plank or log sides, flooring, sometimes roofed, sandbags, gabions Dimensions: 5-15+ feet per side; traverses of varying length, relief Features: Access door or trench Situation: Associated with prepared artillery positions, siegeworks Class Seven: PERSONAL FIELD SHELTER Includes: discrete fox holes, picket or skirmish holes, command holes, slit trenches, "rifle pits" Builders: typically sited by individuals in action Type of construction: hole with earth thrown to front or shallow trench, rear-ditched Materials: earth, sometimes wood or stone fill, typically not revetted Dimensions: 2-5 feet relief, 2-8 feet width of parapet Features: discontinuous, arrayed in pattern of unit, shelters 1-3 persons, slit trenches shelter 4-10 persons Situation: picket or skirmish lines, holes associated with rapid entrenchments Page 4 of 6 MOC Earthworks Tour 4
Class Eight: DEFENSES OF CONVENIENCE Includes: stone walls, piled stone breastworks, sunken roads, railroad cuts/fills, often enhanced by digging Builders: pre-existing features adapted to combat or constructed ad hoc by soldiers Type of construction: various Materials: stone, wood, earth Dimensions: various Features: walls, barricades Situation: meeting battles, stony ground, shallow topsoil Further Reading Christopher Duffy, Fire and Stone: The Science of Fortress Warfare 1660-1860. London: David and Charles, 1975. Paddy Griffith, Battle Tactics of the Civil War. New Haven: Yale University Press, 1989. Edward Hagerman, The American Civil War and the Origins of Modern Warfare. Bloomington: Indiana University Press, 1988. O. E. Hunt, "Entrenchments and Fortifications," in Francis Trevelyan Miller, ed., The Photographic History of the Civil War, vol 5, 194-218. W. C, Johnson and E.S. Hartshorn. "The Development of Field Fortifications in the Civil War" in Professional Memoirs, Corps of Engineers, United States Army and Engineer Department at Large, 7, September-October 1915, 570-602. Robert K. Krick, "Fire and Stone." In Touched by Fire: A Photographic Portrait of the Civil War. Edited by William C. Davis. Boston: Little, Brown, 1986, Volume 2, 111-58. David W. Lowe, Field Fortifications in the Civil War in North and South Magazine 4, no. 6 (Summer 2001). Dennis Hart Mahan, A Summary of the Course of Permanent Fortification and the Attack and Defense of Permanent Works. Richmond: West and Johnston, 1863. Dennis Hart Mahan, Treatise on Field Fortification, Containing Instructions on the methods of laying out, constructing, defending, and attacking Intrenchments, with the General Outlines also of the Arrangement, the Attack, and the Defense of Permanent Fortifications. New York: John Wiley, 1863. James St. Clair Morton, Memoir of American Fortification. Washington: 1859. Noah Andre Trudeau, "The Walls of 1864: Field Entrenchments Saved Robert E. Lee's Army--and Grant's as Well." MHQ: The Quarterly Journal of Military History, 6, Winter 1994, 23-31. Arthur L. Wagner, Hasty Entrenchments in the War of Secession in Journal of the Military Service Institution of the United States, 22, February 1898, 225-46. Page 5 of 6 MOC Earthworks Tour 5
Detail showing fortifications at Cold Harbor in the vicinity of the National Park Cold Harbor Unit. From Michler map series (8 = 1 mile), NARA Record Group 77 G204-33 through G204-60. The topographical engineers depicted principal features but were unable to portray the complexity found on the ground. Page 6 of 6 MOC Earthworks Tour 6