Unnecessary casualties are caused by the practice of putting a single row of sand bags along the top of a parapet for temporary purposes of concealment, as it gives a faulty idea to the men in the trench as to the real height of the parapet. The parados gives protection from the effect of shell fire bursting behind the trench, and should be made fire-proof as soon as possible, although it is not necessary unless concealment is possible to level it down in a similar manner to the parapet. As a matter of fact, it should be at least a foot higher than the parapet, thus providing a background for the parapet. It has been known to happen that when the occupants of a trench have been reached by the enemy they have vacated their trench and used the parados as a parapet, much to the surprise and disgust of the enemy. In a high and irregular parados, places could even be found which when not used steadily provide unexpected and safe observation and sniping posts, but care must be taken that they are not used too often. If a trench were used merely for firing, 4½ feet from bottom of trench to top of parapet would be a sufficient depth. During attack, however, when fire from loopholes is too restricted, exposure of head and shoulders over the parapet becomes necessary, but it is not necessary to expose men moving along the trench and not actually firing. If the trench should be 7´ or 8´ deep, you must provide a platform at the bottom of the front wall 1¼´ wide and 4½´ from the top of the parapet. This is called a fire-step. The rest of the trench can be deepened to any desired depth, depending on the energy displayed. If of an extraordinary depth, steps must be cut to the fire platform. In a great many different parts of the Western Front, especially Belgium, it was found that after digging to a depth of one to three feet water was encountered to such an extent that it became impossible to dig any sort of a trench which would give adequate protection to the men involved. [Illustration: _FIRE TRENCH._ _LINK TRENCH._ _SUPERVISION TRENCH._] When these conditions are run into, breast work parapets must be artificially built up above ground level with soil, sods and sandbags, supported by sandbags, hurdles or close wire netting, revetment and stakes. The same principles of thickness, depth, width, slopes, and in fact everything that applies to a dug-in trench, applies to breast works. [Illustration: _A--Link Trench, minimum length 5 ft._ _“S” & “T” TRENCH._]