Loopholes are made wherever head cover is provided. Where the enemy's trenches are close, there is considerable danger in using them. Collective firing takes place over the parapet. When loopholes are used they should face half-right or half-left and not directly to the front. [Illustration: Plate 16.--Method of draining trench.] [Illustration: Plate 17. Details of trench drainage.] [Illustration: Plate 18. Detail of trench drainage.] [Illustration: Plate 19.--Overhead cover.] [Illustration: Plate 19a.--Overhead cover.] [Illustration: Plate 20.--Overhead cover.] [Illustration: Plate 20a.--Overhead cover.] The disadvantages of loopholes are: 1. The difficulty of concealing firing points. Loopholes give the enemy's snipers an easy mark. 2. They lessen the number of rifles that can be used at a given point. 3. The necessary head cover makes it difficult to get out of the trench quickly. 4. Damaged head cover often spoils a good firing point. The three types of loopholes are: 1. Narrowest point of the opening nearest the marksman. This type is most difficult to conceal, much of the parapet thickness is cut away and, if of hard material, tends to deflect the bullets into the firer's face. This defect may be remedied somewhat by stepping the surface of the loophole. 2. Narrowest point to the front. Easiest to conceal but gives a limited field of view. 3. Narrowest point midway between the front and rear. A compromise between the first two types. The following general remarks on the construction of loopholes are taken from a work based upon the experience gained during the war in Europe: 1. The angle of splay is usually 60 degrees. The thicker the parapet the smaller must be the angle of splay. [Illustration: Plate 21.--Types of loopholes.] 2. The marksman holds his rifle in a line connecting the right shoulder, the eye and the object, hence most of the body lies to the left of the rifle. The loophole should be made to the right, with a niche in the wall of the parapet from the hip to the armpit, to bring the left shoulder well forward. It will be found that this permits the right elbow to be placed on the edge of the parapet. [Illustration: Plate 22.--Methods of constructing loopholes with sandbags.] 3. Box loopholes with screens or blindage may be used, but should be placed by a skilled marksman. The great disadvantage is that the enemy notes these parapet alterations. Steel loophole plates are now provided for this type of loophole. As the Germans sometimes use a steel bullet with great penetrating power, it is advisable to place two plates together to insure protection. 4. With every precaution that may be taken it is difficult to conceal a loophole. A good plan is to deceive the enemy by using painted sandbags and preparing plenty of dummy loopholes. 5. The minimum width of loopholes should be 2-1/2 inches. If narrower than this, it is impossible to use both eyes to judge distances correctly.