(Second) A trench that is sufficiently narrow will localize the effect of a bursting shell or bomb and minimize the effectiveness of hostile fire, which must have a high degree of accuracy to be effective. But the quicker over the ground the shorter the period of danger, and shell fire of any degree of accuracy will substantially narrow one of these narrower trenches, damaging the walls and causing casualties and other obstructions which will render passage impossible with either one or two results. Delay caused at a critical moment, or the occupants trying to obtain a passage up the trench in order to take any part in the fighting, would have to come out into the open sooner than necessary. The shelling of the C. T.’s usually is heavier for perfectly obvious reasons during an attack and when rapid transit through them is of the utmost importance. A narrow trench generally takes as long to dig as one of the wider type, owing to the restricted area in which to work. (Third) If invisibility be possible, it is an excellent feature, but in nine hundred and ninety-nine cases out of a thousand it is hardly possible. An observed C. T. indicates the position and direction of supports, stores, reserves, dugouts, etc. This fault can be corrected to a certain extent by the careful use of the contours, dead ground, sunken roads, and all natural features, such as woods and hedges. Artificial cover may and does assist concealment, but sooner or later hostile aerial observation and photographs disclose the position of more easily concealed things than an excavated C. T. It is frequently the shadow at the bottom of a trench which gives its position away to aircraft, and the narrower the trench, the more prominent is the shadow. The soil, which is generally a different color from the surface soil, must be thrown up on either side as time does not allow it being carried away. Unless in a place of artificial cover through the length of the C. T., it is usually necessary to admit the impossibility of concealment and utilize time more profitably by taking protective measures. Rapid transit to a fire-trench is of greater importance than rapid transit from a fire-trench, and the importance of protection is greater as the fire-trench and its dangers are approached. Methods of construction should be based on this idea and the arguments given above. SKETCH OF TRENCH SYSTEM This sketch shows a double-traffic communication trench leading (5 ft. wide) from reserves and H. Q. to a loopholed island-traverse about 30 yards behind the support line. At this island-traverse, single-traffic C. T. branches off to various sectors of the support line; the main C. T. leading on (from 3 to 4 feet wide) uninterrupted through the support line to loopholed island-traverse “E,” about 30 yards behind the firing line. At this island-traverse the main C. T. breaks off into single-traffic C. T. 3 feet wide. Each leads to various sectors of the firing line. [Illustration: SECTION I