the spirit and determination of the force that is
being pursued. Generally speaking, Rear Guard fighting against an
unexhausted enemy is the most difficult and most dangerous of all
military enterprises. When a Rear Guard halts to fight it is being
separated every minute from the Main Body, which is moving away from
it, while every minute brings reinforcements to the enemy. The work
requires great tactical skill, as it is the duty of the commander to
delay pursuit by occupying positions from which he withdraws at the
last moment, without becoming involved in a general engagement, from
the meshes of which it may be necessary for the Main Body to return and
extricate him. The work also requires great moral courage, as it is
the duty of the commander to risk the loss of his force if by so doing
he is adopting the only means of saving the Main Body.

STRENGTH.--The strength of the Rear Guard will depend upon the energy,
strength, and closeness of the pursuit, the condition of the Main Body
(and whether it is withdrawing voluntarily or upon compulsion after an
unsuccessful engagement) and upon the nature of the country, but it
will generally amount to not less than {120} one-fifth or more than
one-third of the whole force, and will be selected, as a rule, from
those who have been least severely engaged.

COMPOSITION.--Its composition depends upon the work to be performed,
and this calls for detachments of all arms of the land service, in
addition to _Aircraft_, which can prevent surprise by reconnaissance
over the hostile area and can harass the pursuing columns by day and by
night by fire-action with Lewis guns and bombs. _Mounted troops_ are
required to extend the area watched and to prolong the resistance by
reason of their superior mobility, in addition to their counter-action
as cavalry. _Artillery_ are required to open long-range fire on the
enemy's columns and so to cause delay by deployment; and to concentrate
upon them while in, or emerging from, a defile. _Infantry_ and
_Machine-gun Platoons_ are required for prolonged fire-fights and local
counter-attacks, during which sudden bursts of machine and Lewis-gun
fire will do the greatest execution. _Engineers_ provide sappers for
the creation of obstacles and traps, and for the demolition of bridges
and viaducts. _Mechanical Transport_ may be required to add to the
mobility of the infantry. The _Medical Service_ is called upon to
provide attention and ambula