The advance guard is a detachment of the main body which precedes and covers it on the march. The primary duty of an advance guard is to insure the safe and uninterrupted march of the main body. Specifically its duties are:
1. To guard against surprise and furnish information by reconnoitering.
2. To push back small parties of the enemy and prevent their observing, firing upon, or delaying the main body.
3. To check the enemy's advance in force long enough to permit the main body to prepare for action.
4. When the enemy is encountered on the defensive, to seize a good position and locate his lines, care being taken not to bring on a general engagement unless the advance guard commander is empowered to do so.
5. To remove obstacles, repair the road, and favor in every way the steady, march of the column.
The strength of the advance guard will vary with the proximity of the enemy and character of the country; for a regiment it will generally consist of from two troops to a squadron, for a squadron of one troop; for a troop of from a section to a platoon. The advance guard commander is responsible for the proper performance of the duties with which it is charged and for its conduct and formation.
The advance guard provides for its security and gains information by throwing out to the front and flanks smaller bodies: Each part must keep in touch with the unit from which it is sent out. An advance guard is generally divided into a reserve and a support; where it consists of less than a squadron, the reserve is generally omitted.
The support sends forward an advance party, which, in turn, sends forward a point. In small advance guards the point precedes the advance party about 350 yards, the advance party the support about 500 yards, and the support the main body about 600 yards. Where advance guards are large enough to require a reserve these distances are increased about one-fourth, the reserve following the support, the main body following the reserve at a distance varying from 500 to 800 yards.
Unless the country to the flanks is distinctly visible from the roads for a distance of what may be said to be effective rifle fire, approximately 1,000 yards, flanking patrols of two or three men each should be sent out from the advance party, and, when in proximity of the enemy, in addition from the support. When the nature of the country is such that patrols may move across country, without unduly delaying the march these patrols should march at a distance of from 500 to 600 yards from the flank of the body from which detached. For the examination of any object, such as a wood, buildings, etc., examining patrols should be sent out from the main body. The usual method of protecting the flanks, particularly when the country is at all cut up or difficult, is to send out patrols from time to time to some point from which a good outlook can be obtained, or which will afford protection to the enemy. These patrols remain in observation, observer being dismounted, his horse held by another trooper until the advance guard has passed, when they rejoin the nearest subdivision, as quickly as possible working their way to that to which they belong during the halts or by riding up the side of the road. By sending out a succession of small patrols in this manner the flanks are protected. Should the advance party become depleted, it must be reenforced from the support.