On the battlefield, natural features that screen and shelter should be utilized as much as possible, as they possess the following advantages over artificial works: (_a_) Their organization demands less work. (_b_) Concealment is easier. (_c_) From their nature, it is difficult for the enemy to estimate, for a given length, the number of men sheltered. They possess, however, certain disadvantages: (_a_) The protection is sometimes so excellent that, morally as well as materially, it becomes difficult to leave the shelter. Example: quarries with obstructed exits. Therefore, good judgment must be exercised in the selection. (_b_) Some of them are too visible. Example: large hedges. In this case their range can be easily found. As a general rule, do not occupy them uniformly and do not change the appearance of the organized parts. Organization of the cover: To organize the cover which protects troops from fire, construct suitable positions for firing and resting. To utilize the screens which merely hide the troops without protecting them from fire, dig trenches behind these screens in the following manner: (_a_) Choose the points which give the best field of fire. (_b_) Construct cover for firing. (_c_) Construct a shelter. The constructions are usually "individual" in the first period of work; afterwards, they are organized "collectively." The covers are: (1) for riflemen lying down, (2) for riflemen sitting down, and (3) for riflemen standing up. [Illustration: Plate 27a.--Use of the cover without improvement.] [Illustration: Plate 27b.--First period.] [Illustration: Plate 27c.--Second period. Progressive improvement of the cover.] INDIVIDUAL ORGANIZATION OF NATURAL COVER Examples of hasty individual cover behind trees, bushes, or branches: (_a_) Fallen tree (logs or branches), the height of which is at a maximum of 1 foot above the ground: (_b_) Fallen tree, the top of which is more than 1 foot above the ground. [Illustration: Plate 27d.--First period.] [Illustration: Plate 27e.--Second period] [Illustration: Plate 27f.--Third period.] Wood which does not afford sufficient protection against bullets must be reinforced by earth at the right and against the cover 1 foot behind. Plates 27d, 27e, and 27f show the progressive improvement of the cover. [Illustration: Plate 27g.--Sharp ridges, furrows, or top of a crest at the end of a gentle slope.] Examples of hasty individual covers behind a furrow, a crest, a heap of sand or earth: Dig the ground as near as possible to crest _A_ of the furrow in the manner indicated for the cover installed behind a fallen tree more than 1 foot high. [Illustration: Plate 27h.--Narrow furrows.] Use the earth excavated between furrows _A_ and _B_ to build up the earth between furrows _B_ and _C_ and fill up furrow _C_; continue afterwards as for the sharp ridge. [Illustration: Plate 27i.--Low wall of earth, or earth and sand heaps, more than 2 feet high (two methods, _A_ or _B_).]