euvre is
specially convenient when attacking a Rear Guard, for the latter cannot
fulfil its mission once it has been turned" (Marshal Foch).

{122}

_The Main Guard fights for time_. If the withdrawal is more or less
unmolested, or if such pursuit as is offered can be dealt with by the
Rear Party, the Main Guard can continue its march, taking care not to
close in on the Main Body; and while falling back it can demolish
bridges, create obstacles, prepare ambushes, and so on, employing all
devices (within the laws of war) for delaying the enemy. When hotly
pursued it must gain time at all costs for the army it is covering, and
must not allow itself to be driven back on to the Main Body; or it will
hamper that force and cease to protect it. Time can be gained by
compelling the enemy to halt to reconnoitre a position, by making him
deploy into attack formation, and by making him go out of his way in
order to envelop a flank. But before an attack reaches a position in
such strength as to ensure success, and before the enveloping force can
achieve its object, sub-divisions of the Main Guard will withdraw in
succession under covering fire from those still in the line, which also
withdraw in their turn under covering fire from the sub-divisions in
their new positions, to tactical points further back, from which again
they cover the withdrawal of the forces which had protected their own
movement.

Certain points must be noted about the positions chosen for these
successive fire-fights, and the choice of the positions is so difficult
that an experienced staff officer should be specially detailed for the
work, Positions chosen must be in the enemy's way and the lines of
withdrawal to them must not converge; they must be easy to defend and
difficult to attack; the flanks must be secure from direct attack and
effective enfilade fire, necessitating a wide detour (and consequent
gain of time from the enemy) before they can be threatened; long-range
artillery fire on the lines of approach should be possible in order to
delay and break up the enemy's advance; and each position chosen for
the next line of resistance should be unseen by the {123} pursuing
enemy, and sufficiently far away from the line last occupied to induce
him to resume his march formation. This will necessitate a repetition
on the part of the enemy of all the stages of the attack--the discovery
and the report on the position, the decision to attack, and the
de