One of the first things to be insisted upon in training a man is that he learn the use of COVER. He must learn not only that cover is necessary, but also what constitutes effective cover of various materials. The most common form of cover is that afforded by piled up earth. A rifle bullet fired at short range will pierce about forty inches of earth so that nothing less than thirty-six inches can be considered as giving protection from ordinary bullets. Where sand can be obtained ten inches less will suffice. Ordinary turf is not nearly so good and nothing less than five feet in thickness is sufficient. Bricks are effective. If they are placed end on giving a thickness of nine inches this will be found sufficient so that a man can feel fairly secure from rifle bullets standing behind an ordinary brick wall. Where wood is used much depends on its degree of hardness; thirty inches for hardwood and forty-five for softwood can be taken as affording complete protection. Any of the harder substances such as iron and steel, etc., are preferable, but they can seldom be obtained. Of ordinary iron plate three-fourths inch is necessary and less for the different varieties of steel. Usually several of these media must be used. Boards can be arranged with stones and sand or litter, etc., between them. The point to be remembered is that the required thickness must be obtained, not at the base of the cover but at the top, to support which a much larger base will usually be required. When a man has learnt what thickness of materials he needs to have to protect his life, it will be a good thing to take him out and let him see how far bullets are able to pierce these media by actually firing at them from point blank range. That will give him a respect for bullets and impress the lesson on him. But he must also be told that cover that protects is only half what is required. It must be such as to allow him to become offensive while giving him defence. The problem is a simple one in actual trenches, where he has no alternative but to build them continuously and then fire over the top or through loopholes of steel. But when more open fighting develops he must learn that his business is not only to get reasonable protection for his own body but to be able to bring his rifle to bear on the enemy. This necessitates a certain amount of exposure. Certain devices have been developed during this war to allow a man to fire his rifle from beneath the parapet of the trench by means of specially adapted periscopes. These are of great use for snipers but cannot be used by all the men.