in fortification, is a small ditch from 15 to 20 feet broad, made in the middle of a large dry ditch, serving as a retrenchment to defend the same, or otherwise to let water into it, when it can be had during a siege.
When there is a cunette, there should be a caponniere to flank it.
Defilement, in fortification, is the art of disposing all the works of a fortress in such a manner, that they may be commanded by the body of the place. It also includes the relative disposition of the works, and the ground within cannon shot, so that the one may be discovered, and the other not observed.
Demi-gorge, is half the gorge, or entrance into the bastion, not taken directly from angle to angle, where the bastion joins the curtain, but from the angle of the flank to the centre of the bastion, or rather the angle the two curtains would make were they protracted to meet in the bastion. Mr. Landmann determines it to be the line which is formed by the prolongation of the curtain meeting the oblique radius.
Demi-lune. See [Ravelin].
Descents in fortification, are the holes, vaults, and hollow places made by undermining the ground.
Descents into the ditch or fossé, are boyaux or trenches effected by the means of saps in the ground of the counterscarp, under the covert way. They are covered with madriers, or hurdles, well loaded with earth, to secure them against fire. In ditches that are full of water, the descent is made even with the surface of the water; and then the ditch is filled with fagots, fast bound, and covered with earth. In dry ditches the descent is carried down to the bottom; after which, traverses are made either as lodgments for the troops, or to cover the miner. When the ditch is full of water, the descent must be made over its surface; which is done by securing it with blinds or chandeliers, from being enfiladed, or by directing the course of the descent from the point of enfilade in the best way you can.
Detached bastion. See [Bastion].
Detached redoubt. See [Redoubt].
Ditch, in fortification, is a large deep trench made round each work, generally from 12 to 22 fathom broad, and 15 to 16 feet deep: the earth dug out of it serves to raise the rampart and parapet. Almost every engineer has a particular depth and breadth for ditches; some are for narrow ones and deep, others for broad ones and shallow; and it is most certain that ditches should be regulated according to the situation. In regard to wet and dry ditches, almost all authors have given it in favor of the latter; and we shall only add, that the best of all are those which can either be filled or kept dry at pleasure.