641. The strength of the advance guard varies from one-twentieth to one-third of the main body, depending upon the size of the main body and the service expected of the advance guard.
642. The formation of the advance guard must be such that the enemy will be met first by a patrol, then in turn by one or more larger detachments, each capable of holding the enemy until the next in rear has time to deploy before coming under effective fire.
643. Generally an advance guard consisting of a battalion or more is divided primarily into the _reserve_ and the _support_. When the advance guard consists of less than a battalion, the reserve is generally omitted.
644. In an advance guard consisting of two battalions or less, the reserve and support, if both are used, are approximately equal; in larger advance guards, the reserve is approximately two-thirds of the whole detachment.
In an advance guard consisting of one battalion, the machine guns, if any, form part of the reserve. In an advance guard consisting of two or more battalions, the machine guns form part of the support.
645. The _support_ sends forward an _advance party_. The _advance party_, in turn, sends a patrol, called a _point_, still farther to the front. Patrols are sent out to the flanks when necessary. When the distance between parts of the advance guard or the nature of the country is such as to make direct communication difficult, connecting files march between the subdivisions to keep up communication. Each element of the column sends the necessary connecting files to its front.
646. A battalion acting as an advance guard should be formed about as follows: The _reserve_, two companies; the _support_, two companies; the _advance party_, three to eight squads (about a half company), depending upon the strength of the companies and the reconnaissance to be made; the _point_, a noncommissioned officer and three or four men. Or the reserve may be omitted. In such case the advance party will consist of one company preceded by a strong point. The remaining companies form the support.
647. The distances separating the parts of an advance guard vary according to the mission of the whole force, the size of the advance guard, the proximity and character of the enemy, the nature of the country, etc. They increase as the strength of the main body increases; they are less when operating in rolling, broken country than in open country; when in pursuit of a defeated enemy than against an aggressive foe; when operating against cavalry than when against infantry.