589. _Hasty cover._ With the intrenching tool, troops can quickly throw up a low parapet about 3 feet thick which will furnish considerable cover against rifle fire, but scarcely any against shrapnel. Such cover is frequently of value to an attack that is temporarily unable to continue. In time, and particularly at night, it may be developed into a deep fire or cover trench. 590. _Fire trenches_ should be placed and constructed so as to give a good field of fire and to give the troops protection behind a vertical wall, preferably with some head or overhead cover. They should be concealed or inconspicuous in order to avoid artillery fire or to decrease its accuracy. They should have natural or artificial communication with their supports, but in establishing the trace this is a secondary consideration. The simplest form of fire trench is deep and narrow and has a flat, concealed parapet. (Fig. 1.) In ordinary soil, and on a basis of two reliefs and tasks of 5 feet, it can be constructed in about two hours with intrenching tools. This trench affords fair cover for troops subjected to fire, but not actually firing. When it is probable that time will permit elaboration, the simple trench should be planned with a view to developing it ultimately into a more complete form. (Figs. 2 and 3.) Devices should be added to increase the security of the trench and the comfort of the men. Where the excavated earth is easily removed, a fire trench without parapet may be the one best suited to the soil and other conditions affecting the choice of profile. (Fig. 4.) The enemy's infantry, as well as his artillery, will generally have great difficulty in seeing this type of trench. In very difficult soil, if the time is short, it may be necessary to dig a wider, shallower trench with a higher parapet. [Illustration: Plate V.] Head cover, notches, and loop holes are of value to troops when firing, but many forms weaken and disclose the location of the parapet. Filled sandbags kept in the trench when the men are not firing may be thrown on the parapet to form notches or loopholes when the troops in the trench open fire and concealment of the trench is no longer necessary or possible. By the use of observation stations the maximum rest and security is afforded the troops. Stations are best located in the angles of traverses or at the end of the trench. 591. Where the nature of the position makes it advisable to construct traverses at regular intervals it is generally best to construct a section of trench for each squad, with traverses between squads. (Fig. 5.) 592. _Cover trenches_ are placed as closely as practicable to their respective fire trenches. Where natural cover is not available, each fire trench should have artificial cover in rear for its support--either a cover trench of its own or one in common with an adjoining fire trench.