have also to be carried out, and communication with the Main
Body has to be maintained. For the purposes of reconnaissance and
communication Aircraft are even more effective than in Advanced Guard
work, while observation patrols supplement and confirm the reports of
aerial observers. The work of protection varies with the nature of the
country through which the Guard and the Main Body are moving at the
particular time. In open country the Flank Guard may be keeping pace
with the Main Body at a regularly maintained interval, and on parallel
lines. In close country, and in hilly or mountainous districts, it may
be necessary to occupy a successive series of tactical positions on the
exposed flank, any of which can be reinforced and held at need to
safeguard the passage of the Main Body. In order that the whole column
may be protected, from the head of the Main Body to the train in rear,
unbroken touch must be maintained both with the Advanced and the Rear
Guard, and incursions between these forces and itself must be prevented
by the Flank Guard.

{116}

In addition to the protection of a column on the march, Flank Guard
work is of the highest importance on the Lines of Communications and in
the protection of Convoys. On the _Lines of Communications_ raids from
the air or land may always be expected in Manoeuvre Warfare, and one
flank is usually more vulnerable than the other. A _Convoy_, when
parked, is liable to attack from any quarter; and when on the march it
may be assailed from any direction, especially when the adversary can
detach mounted troops, or infantry rendered mobile by motor transport,
or raiding bodies carried in Aircraft. Frequently, however, one flank
only of the Lines of Communications is vulnerable owing to the
geographical or tactical situation, and the work of protecting traffic
or Convoys on the Lines of Communications is Flank Guard work, with due
precautions against surprise from all quarters, the Main Guard
remaining with the Convoy and securing its safe arrival at its
destination, rather than seeking an encounter with the enemy. The most
efficient way to protect a Convoy is to piquet the road daily with
troops sent out from posts on the line; but when it is necessary to
send a Convoy by a route which cannot be protected in this way a
special escort must be provided. The commander of an escort will not
engage the enemy if his task can be accomplished without fighting. If
fighting is