mutually
support each other by fire. The gaps between the posts must be covered
by the fire of the garrison of the posts, and machine guns may also be
sited to bring fire to bear from positions in rear and to the flanks"
("Infantry Training, 1921"). This principle must govern the choice of
the position to be defended as well as the organisation of the position
for defence, and troops detailed for the defence of an area must
continue to improve the defensive arrangements in that area until such
time as the offensive is resumed.

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troops when withdrawn from the front line.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 absorb