The strength and composition of the rear guard is the next item, and this is regulated by its function of supervision of the retirement of the picquets.
Such being the case, it appears that, in no circumstances, should a large force be detailed as a rear-guard. There is not space in a narrow valley for a strong rear-guard to manœuvre, so that it will merely afford the enemy a good target, without corresponding advantage; besides, the rear-guard can, if necessary, be continually reinforced by incoming picquets.
A rear-guard, then, should rarely include more than four companies of infantry, and in the circumstances under consideration, may be weaker.
Though cavalry may be useful for the delivery of a counter-attack, the horses afford an easy mark, whilst its presence with the rear-guard may cause the enemy to keep to the hills instead of descending into the valley, where they will be more vulnerable. Cavalry, it seems, should, therefore, not be added to the rear-guard infantry.
Mountain guns may be of assistance to picquets in distress, or in the delivery of a counter-attack, but they should, both for their own security, and to prevent waste of ammunition, be kept well back. In the present case the rear-guard is not likely to be harassed, so no artillery need be included.
A rear-guard does not require technical troops, but some hospital riding mules, etc., may be allotted for rapid transference of wounded.
The total deductions from the fighting force of the column will therefore be:—
Advanced Guard. Six companies Infantry, bulk of one company S. and M.
Escorts, etc. Three or four companies Infantry.
Rear-guard. Two or three companies, with machine guns.
In all about one and a half battalions, one company sappers and miners. There remain three and a half battalions, one mountain battery, one squadron, and the administrative services, at disposal.
The order of march of the main body can now be dealt with.