Parapets

(Ital. parapet to , “breast guard”). In fortifications, are breastworks, walls, or bulwarks of earth, brick, wood, iron, stone, or other material. The battlement around a flat roof, or the railing of a bridge is also called a parapet. The parapets of field-works are always made of earth, which is also largely used in permanent fortifications. Earth has great advantages for this purpose, being readily obtained, easily handled, and affords good cover on account of the absence of splinters and flying fragments when struck by a shot. The presence of rock or large gravel in the earth is objectionable for this reason. Of the different earths, sand, hard clay, tufa, etc., resist penetration better than rich soils. The profile of the parapet is determined by its location and purpose. The earth to form it is taken from the ditch, which is sometimes in front and sometimes in rear. In inclosed works, or works built at leisure, the ditch is always on the outside, leaving the natural surface for the parade. Works built hastily, or under fire, have the ditch on the inside. In this way cover is more rapidly obtained. This form of parapet is used in all the trenches in siege operations and the temporary lines thrown up on the field of battle. The command of a parapet is the height of the interior crest above the site. For isolated works the command should be at least 8 feet, as the chances of a succe ful resistance increase with the command. The profile of a parapet is a section taken at right angles to its length. In infantry parapets the banquette is the bank of earth in rear of the parapet, on which the troops stand to deliver their fire. This is usually about 4 feet wide, and about 4 feet 3 inches below the interior crest. The height of the banquette depends upon the command of the parapet. The interior slope of the parapet, against which the soldier leans in firing, has a slope of 3 on 1. To support the earth at this inclination a revetment of sand-bags, fascines, gabions, sod, pis a, or plank, is used. The superior slope of the parapet is usually 1 on 6. It should be steep enough to give a fire just above the farther edge of the ditch, but not so steep as to weaken the parapet. The exterior slope is 1 on 1, or the natural slope of the earth. If it is made steeper than this it will be beaten down by the projectiles of the enemy; if le steep, it will offer a le obstacle to open a ault. The berme , or space between the foot of the exterior slope and the edge of the ditch, is objectionable, in offering a breathing-place to the enemy in the a ault, but it is usually nece ary to prevent the weight of the parapet from crushing in the scarp. The dimensions of the ditch are regulated by the amount of earth nece ary to form the parapet. The scarp and counterscarp are made as steep as the stiffne of the soil will allow. As a general rule, the depth of the ditch should not be le than 6 feet, and its width should not be le than 12. The greatest width is regulated by the superior scope of the parapet, the line of which produced should not pa below the crest of the counterscarp. In excavating near a salient it will be found that more earth is furnished than in re-enterings. On this account the width of the ditch is usually made variable, being le at the salients than elsewhere. The thickne of a parapet is the horizontal distance between the interior and exterior crests. This thickne should be one-half greater than the penetration of the projectiles it is designed to resist. As the rifled guns now in use have much greater penetration than the smooth-bores of former times, a proportionate increase in the dimensions of parapets has become nece ary. The parapets of semi-permanent field-works are usually calculated to resist the fire of siege-guns; those of permanent works to resist the most powerful ordnance in use. The trenches so much used in modern times to cover operations of armies in the field are shallow ditches, with the earth thrown outwards.