Lines, Redan

Development of redan lines was traditionally attributed to the great French engineer Vauban who employed a series of redans connected by curtains laid out on right lines as the basic pattern for lines of circumvallation that protected the camps and depots of a besieging army from enemy forces attempting to relieve a besieged fortification. This pattern was adapted to general lines constructed for the purpose of closing extended stretches of ground; many of the lines constructed by the French during the early eighteen century wars in Europe to close their frontiers or protect fertile country from hostile foraging were laid out as redan lines. When laid out on a level site Vauban's redan line spaced redans about 200 yards apart (from capital to capital of the line's redans) with the capital of each redan about 40 yards long. Gorges of the redans were about 60 yards on the general line of the curtain and the curtain was about 170 yards long. Passages through the curtains were covered by lunettes laid out as the redans, but with their faces cut off at a distance of 36 yards from the capital to form flanks which were terminated about 10 yards from the line of the curtain. Angles in a redan line could also be covered by small bastions with faces about 50 yards long, capitals 50 yards taken from the salient of the bastion to the angle formed by prolongations of the curtains, and flanks 20 yards long.

Most pre-Civil War period manuals maintained Vauban's dimensions for redan lines while suggesting only very minor adjustments. J. S. Macaulay described redan lines as having redans 260 yards apart with 30 yards of demi-gorge and capitals 44 yards long. He suggested that the redans be positioned at 200 yards (rather than 260) intervals to bring the prolongation of the redan capitals within musket range of collateral redan faces. D. H. Mahan described a redan line that had the redan capitals 180 yards apart, redan faces 60 yards long and salients opened 60°, which gave a distance of 160 yards from redan salients to collateral re-enterings where redan faces joined the straight curtains. Rather than setting down an exact distance between salients in redan lines A. F. Lendy described a method that could be used to insure that ground in front of each redan salient was well protected by fire delivered from the faces of collateral redans. This method took a line perpendicular to the face of a redan and projected from the salient angle of the redan to the maximum effective range of the small arms that would be used to defend the line. From that point exterior to the line a second line was projected perpendicular to the general line of the curtain to mark the capital of a second redan. This insured that fire from each face was strike ground along the weakest point of the redan, that is, along the prolongations of the redans' capitals.

Redan lines were considered to have a relatively great number of defects that limited their usefulness: the ditches were not flanked and could not be seen from the interior crest; the faces of the redans were protected by a very oblique (and therefore less certain) fire delivered from the curtains; salients of the redans produced large sectors without fire that were not completely defended by fire from collateral redans. Faces of the redans crossed their fire with that of the curtain at a distance from the curtain and could not participate in the close defense of the curtains. Once an attacking body of troops reached the ditch it could not be reached by fire delivered from the parapet while ground in front of the ditch was not adequately protected by over-lapping or crossing columns of fire. The greatest concentration of fire was projected over ground in front of the curtains while the most vulnerable points of attack, the redan salients, were protected by the least amount of fire delivered at the longest ranges from the parapet. Many manuals suggested that these defects could be partially mitigated by breaking the curtains forward to form two faces that could better project columns of fire across the redan faces and salients, but. this modification in the trace converted redan lines into tenaille lines, a distinct type of line that must be treated separately.

As with all temporary fortifications, redan lines that were actually constructed tended to deviate from the basic prescribed pattern and dimensions in proportion to the irregularity of the ground where they were sited influenced, as a matter of course, by the skill of the engineer charged with their design along with the time, material resources, and labor at his disposal. For instance, much of the original entrenched line constructed in 1862 by Captain Charles F. Liernur to protect Mobile, Alabama was laid out as a regular redan line on ground that was very nearly level and did not require any extreme deviations from the basic prescribed pattern. The same held true for the fortifications hastily constructed to cover Montgomery, Alabama, though here the ground was not level, rather, the line was laid out to follow distinct ridge lines and was adjusted, both by adapting the basic redan traces and the uniformity of their intervals, to suit irregularities of the ground. An extreme case is provided by the Confederate line laid out by Confederate Colonel Samuel H. Lockett to cover Vicksburg, Mississippi. Lockett's line followed a series of ridges surrounding the town that were marked by irregular spurs interspaced with deep ravines; Lockett applied irregular redans and lunettes with strong profiles to the advanced points of the ridges and connected them with lines of rifle trenches laid out to command the ridges' slopes and create re-entering angles in the general line that covered the heads of ravines falling away from the ridges. Yet another deviation is found in the Confederate line composing Fort Blakely, Alabama where the Confederate engineers employed a series of irregular triple redans to fortify commanding points along the line while connecting them with relatively straight stretches of continuous parapet.

January, 2003