A rear guard is a detachment detailed to protect the main body from attack in rear. Cavalry is an excellent arm for rear guard duty on account of its mobility. While part of the cavalry is using dismounted fire action, the other part may gallop back and take up a new position. 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. 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. =Section 6. Flank guards.= A flank guard is a detachment detailed to cover the flank of a column marching past, or across the front of, an enemy. It may be placed in position to protect the passage, or it may be so marched as to cover the passage. The object of the flank guard is to hold the enemy in check long enough to enable the main body to pass, or, like the advance guard, to enable the main body to deploy. Like all other detachments, it should be no larger than is necessary, and should not be detailed except when its protection is required. When a flank guard consists of a regiment or less, its distance from the main body should not be much over 5 miles. Practicable communication must exist between it and the main body. The flank guard is marched as a separate command; that is, with advance or rear guards, or both, as circumstances demand, and with patrolling on the exposed flank. =Section 7. Outposts.= Troops not on the march provide for their security by outposts. The general duties of an outpost are reconnoissance, observation, and resistance. The specific duties are: 1. To protect the main body, so that the troops may rest undisturbed. 2. In case of attack, to check the enemy long enough to enable the main body to make the necessary dispositions. During an advance the outposts are usually detailed from the advance guard. During the retreat the outposts for the night usually forms the rear guard the next day. If the command remains in bivouac, the new outpost generally goes on duty at daybreak. The vigilance of outpost troops must be unceasing, but they should avoid bringing on combats or unnecessarily alarming the command. Firing disturbs the rest of troops and, if frequently indulged in, ceases to be a warning. No trumpet signals except "to arms" or "to horse" are sounded, and all unnecessary noises must be avoided.