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.
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.
