As a C. T. leaving a fire-trench gets farther away, the width should be as soon as possible such as will allow two men to pass one another fully equipped without jostling or scraping the sides of the trench, or approximately 4 ft. at the bottom. This width with recesses described later allows rapid transit for troops passing each other in quiet parties and allowing a much greater safety in an emergency when there is no down traffic.
The front is always referred to as “up.”
Another advantage to be gained in the width of the C. T. is in the fact that it is much easier to keep dry and usable. It permits laying of regulation floor boards, allowing enough room on each side of them for the purpose of drainage, and is a means of preventing falling soil from covering the floor boards. Water will not drain off or through soil which is continually trampled on and has become sodden or irregular, and unless the floor boards are kept free from soil, they soon become useless, crooked and immovable. The width of these trenches allows the wind and sun to reach the bottom of the trench, thus helping a great deal in keeping it dry. There is no such thing as a communication trench 18 inches wide at the bottom and 24 inches wide at the top; diggings of these dimensions are nothing more than drains which in an emergency only are struggled through when passing in the open is still more impossible, and they should not be given any consideration whatever as a C. T.
The features required in a communication trench, regardless of the claims of rapid transit and only considering protection, are:
(First) Frequent traverses or turnings to avoid the effect of enfilade fire, to localize the effect of a bursting shell or bomb, to make difficult a hostile advance down the C. T. and to enable bomb parties to resist more easily their advance.
(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.