=6. Crest Line.=--(i) When the objective is a crest line the depth of the beaten zone is greatest, and part of the fire is grazing, when the ground beyond the crest is parallel, or nearly so, to the trajectory of the bullets (Fig. 9, A and B). At close ranges, in this case, there will be behind the crest-line a _defiladed zone, or space not swept by fire_ (Fig. 9, C), greater or less according to the distance from which fire is delivered, the inclination of the line of sight, the extent of the hill top, and the inclination of the reverse slope. (ii) =Position of Supports and Reserve.=--It appears, therefore, _that when the firing-line is placed on the crest of a razor-backed hill_, with steep reverse slopes (Fig. 9, C), supports and reserves will at all ranges be but little exposed to unaimed fire when posted in its vicinity. In other cases, when the crest of a hill is occupied, the vulnerability of supports and reserves will be least if, when the enemy is at long range, they are withdrawn from, and as he approached closed on, the firing-line (Fig. 9, C). =7. Dead Ground= (Fig. 10).--Dead ground is ground on which, owing to its conformation or to the existence of natural or artificial cover, fire cannot be brought to bear from a given locality. The term is thus a relative one, for though an area of ground may be dead in relation to one locality it may be possible to bring fire to bear upon it from another locality, in relation to which it will not therefore be dead. [Illustration: =Fig. 10.=--DEAD GROUND.] CHAPTER III INSTRUCTION IN AIMING Section =15=.--General Remarks. =1. Principles of Instruction.=--The instruction of recruits in aiming and firing should be carried out on a systematic method. The progression of training must in every case lead by gradual steps from simple to more difficult stages. Instructors must necessarily teach by explanation to some extent, but they must limit explanation to short and very clear statements, and rely chiefly upon practical demonstration for training their men. With regard to results they must aim at insuring _accuracy_ in every stage of training before they permit men to attempt _rapidity_. Any sacrifice of accuracy for rapidity must be guarded against carefully and corrected at once. Short daily lectures, followed by questions to test the knowledge of men, should form part of the scheme of instruction. =2. Progression of Instruction in Aiming and Firing.=--The progressive stages of instruction in aiming and firing are set out in a definite order in this and the following chapter which deal respectively with these subjects. Instructors, however, are not bound to follow this order, and may modify it at their discretion.