anes, but as aerial fighting requires
space for manoeuvre hostile machines flying within 3,000 feet of the
ground must be dealt with by machine gun, Lewis gun, or concentrated
rifle fire, except in cases where it is essential to conceal from the
enemy that a certain position or locality is occupied, and where the
troops are so well hidden as to escape detection unless they open fire.
Movement is easily detected by low-flying aeroplanes, and in fair
weather troops can be recognised as hostile or friendly by an observer
at 500 feet, while movements of formed bodies on a road are visible at
5,000 feet. Troops remaining stationary in shaded places may easily
escape observation, and if small bodies in irregular formation lie face
downwards they are difficult to detect, even in the open. When a force
is in movement, detachments move with it to afford protection in every
direction from which interference {101} is possible; and when a force
is at rest, detachments with similar duties secure it from disturbance
and keep off attack until it can be met or developed without
disadvantage. These phases are dealt with under the headings of "THE
ADVANCED GUARD," "FLANK ATTACKS AND FLANK GUARDS," "THE REAR GUARD,"
and "OUTPOSTS."

{102}

THE ADVANCED GUARD

"Fabius, the saviour of Rome, used to say that a commander could not
make a more disgraceful excuse than to plead, 'I never expected it.'
It is, in truth, a most shameful reason for any soldier to urge.
Imagine everything, expect everything."--SENECA, "_De Ira._"

Every moving body of troops must be protected by detachments, the force
detached to precede the advance being known as an Advanced Guard, and
when a body of troops so protected halts, the responsibility for
protection during the halts remains with the troops which have been
protecting the march until they are relieved, the commander of the
Advanced Guard exercising his discretion as to halting at once or
moving forward to occupy a position which may be of more tactical
advantage.

STRENGTH.--The strength of this Guard depends on the proximity of the
enemy, but it must always be strong enough to brush aside slight
opposition, so that the advance of the force it is covering may not be
delayed by small hostile forces, and to resist the enemy, when
encountered in strength, for such time as will enable the force it is
covering to prepare to meet or deliver an attack. No general rule as
to the numerical strengt