Patrols should be sent to the flanks when necessary to reconnoiter a specified locality and should rejoin the column and their proper subdivision as soon as practicable. When the advance party is strong enough, the patrols should be sent out from it. When depleted by the patrols sent out, the advance party should be reenforced during a halt by men sent forward from the support. If it be impracticable to send patrols from the advance party, they will be sent from the support.
Where the country is generally open to view, but localities in it might conceal an enemy of some size, reconnaissance is necessary. Where the road is exposed to fire and the view is restricted, a patrol should be sent to examine the country in the direction from which danger threatens. The object may be accomplished by sending patrols to observe from prominent points. When the ground permits and the necessity exists, patrols may be sent to march abreast of the column at distances which permit them to see important features not visible from the road.
Mounted scouts or cavalry, when available, should be used for flank patrols.
[651.] Cases may arise where the best means of covering the head and flanks of the column will be by a line of skirmishers extending for several hundred yards to both sides of the road, and deployed at intervals of from 10 to 50 yards. A column may thus protect itself when passing through country covered with high corn or similar vegetation. In such case, the vegetation forms a natural protection from rifle fire beyond very short ranges.
[652.] Fixed rules for the strength, formation, or conduct of advance guards can not be given. Each case must be treated to meet conditions as they exist. That solution is generally the best which, with the fewest men and unbroken units, amply protects the column and facilitates the advance.
Rear Guards.
[653.] A rear guard is a detachment detailed to protect the main body from attack in rear. In a retreat, it checks pursuit and enables the main body to increase the distance between it and the enemy and to re-form if disorganized.
The general formation is that of an advance guard reversed.
[654.] Its commander should take advantage of every favorable opportunity to delay the pursuers by obstructing the road or by taking up specially favorable positions from which to force the enemy to deploy. In this latter case care must be taken not to become so closely engaged as to render withdrawal unnecessarily difficult. The position taken should be selected with reference to ease of withdrawal and ability to bring the enemy under fire at long range.
[655.] In large commands artillery and cavalry form a very important part of the rear guard.