CHOOSING A POSITION.—The framework of the modern defence consists of artillery and machine guns; into this framework are fitted the defence posts or defended localities garrisoned by infantry, who are responsible for holding their ground at all costs and for inflicting the greatest possible loss on the enemy. A commander will require a position which affords elasticity for increasing the resistance as the attackers penetrate the defences, and depth will thus be essential. He will require a position wide enough to prevent the whole of his front being masked by a retaining attack of a part of the {84} enemy's forces while a strong flank attack is simultaneously delivered; and in a War of Manoeuvre he will require facilities for the Decisive Counter-Attack.
The depth of the position will develop automatically in a War of Position, but it must always be sufficient to enable troops to assemble in rear of the forward position before moving up and to afford rest to troops when withdrawn from the front line. The width of the position will generally depend upon the strength of the defending force, the guiding principle being to keep about half the force in General Reserve; if, therefore, the remainder of the force is insufficient for the purpose of holding the defences the position is too wide for the tactical requirements of the Active Defence. In Position Warfare, however, a defensive system must necessarily be extended beyond the limits that are practicable in the Active Defence, and the numbers available for the garrison are supplemented by denying ground to the attack by means of obstacles, the removal of which is prevented by machine-gun and rifle fire.
THE OUTPOST ZONE.—For the Active Defence of a position the defensive system will consist of an Outpost Zone and a Battle Position. The Outpost Zone is garrisoned by a protective force which keeps a constant watch on the enemy and absorbs the first shock of the attack, watch being kept by means of well-concealed sentry posts on the Line of Observation, supported by a chain of small self-contained defensive posts, while resistance is offered by a series of self-contained, mutually supporting defence posts on the Outpost Line of Resistance.
THE BATTLE POSITION.—The Battle Position will be established in the area in which the commander decides to fight out the battle and break the enemy's attack. It therefore forms the keystone of the whole defensive position and must be organised in depth to afford elasticity for defensive action. "In principle, in order to protect {85} the battle position from being obliterated by a preliminary bombardment, it should be beyond effective range of the enemy's mortars" ("Field Service Regulations," vol. ii. (1920)).
THE SEMI-PERMANENT SYSTEM.—When a campaign is prolonged in any area without decisive results a War of Position may be developed by one or both of the combatants. In such cases the Outpost Zone is developed into an intricate trench system, with protective avenues leading from front to rear and with deep dugouts to protect the garrison from artillery fire. The Battle Position will probably coincide with the Outpost Zone, the trenches being used for the purposes of observation until the fire positions are manned to resist an assault.
In parts of the line on the Western Front of the Great War, "Pill-box" forts, constructed of concrete, took the place of continuous lines of trenches. These machine-gun forts were garrisoned, according to size, by groups from 5 to 50 strong, and were echeloned in plan, to sweep all approaches, and together to command with their mutually supporting fire the whole area over which they were spread, the intervening ground being entangled with wire so placed as to invite attacking troops into places where flanking fire may be poured into them. The advantages of the pill-box system over the continuous line of strong points are principally defensive. Fewer men are required for them than for the trench systems, and there is less liability of loss from artillery fire. But there are certain grave disadvantages. Well-directed artillery fire is liable to destroy some of the pill boxes, and a direct hit from a heavy gun will possibly put a larger fort out of action, thus crippling the defence by the removal of a peg on which the whole scheme depends. Supports and reserves are necessarily far in rear and must be brought up through the open to repel successful attacks, while a defensive scheme {86} composed entirely on the pill-box plan is less suitable for aggressive action than entrenchments, there being fewer facilities for assembling troops prior to the attack.
COMMON CHARACTERISTICS.—Whatever the system of defence or phase of warfare, every commander must guard his flanks and keep in touch with neighbouring units. He must always be ready to assist a neighbouring commander by enfilade fire or by a relieving counter-attack; or to throw back a defensive flank in the event of a neighbouring post being captured by the enemy. Each post, occupied for the Defence (except in Delaying Actions, where manoeuvre takes the place of a settled resistance), forms a self-contained centre of resistance, capable of all-round fire, and the duty of the garrison is to defend the area allotted to it to the last man and the last round.
THE ACTIVE DEFENCE.—The Active Defence may be considered according to the reason which prompted the commander of the force to occupy the position. It may have been deliberately chosen as a position which the enemy must attack, and in the hope of delivering during that attack a crushing and decisive counter-blow; or it may have been chosen of necessity, to meet an attack by deployment on the ground of the encounter, with the same hope of delivering a decisive counter-stroke when the opportunity arrives.
There is little difference in the steps to be taken by the commander, as in the first case a General Reserve is specially detailed for the counter-stroke; and in the second, the position will be held with as few troops as the tactical situation permits, in order to provide as large a General Reserve as possible for the Grand Offensive. A commander will be influenced by many considerations in his choice of a defensive position:—
(i) The position must suit the plan of operations; it must be "in the enemy's way," and this the commander must be able to judge from the map. It is {87} to be noted that to bar the enemy's way it is not always essential to get astride his lines of advance, as a position on parallel lines, threatening his flank and rear, cannot be ignored by the enemy, unless he is strong enough to detach a part of his force to mask the defender's position, while he proceeds to his objective with his main army. "It was a mistake to assume that in order to cover Turin one had to stand astride the road leading to that town; the armies united at Dego would have covered Turin, because they would have stood on the flank of the road leading to that town" (Napoleon).