If there is a possibility that the rear of the column may be attacked, a rear guard of suitable strength and composition is provided, its conduct is practically the same as that of the rear guard of a retreating force. It generally marches in rear of the trains, those organizations following the combatant troops without distance.
OUTPOSTS
The size and disposition of the outpost will depend upon many circumstances, such as the size of the whole command, the proximity of the enemy and the situation with respect to him, the nature of the terrain, etc.
A suitable strength may vary from a very small fraction to one third of the whole force. For a single company in bivouac a few sentinels and patrols will suffice; for a large command a more elaborate outpost system must be provided. It should be no stronger than is consistent with reasonable security.
The most economical protection is furnished by keeping close contact with the enemy by means of outpost patrols, in conjunction with resisting detachments on the avenues of approach.
The outpost should be composed of complete organizations.
The positions held by the subdivisions of the outpost should generally be prepared for defense, but conditions may render this unnecessary.
Troops on outpost keep concealed as much as is consistent with the proper performance of their duties; especially do they avoid appearing on the sky line.
COMPOSITION
A mixed outpost is composed principally of infantry. The infantry is charged with the duty of local observation, especially at night and with resisting the enemy long enough for the main body to prepare for action. The cavalry is charged with the duty of reconnaissance, and is very useful in open country during the day. If the infantry has been severely taxed by marching or fighting, a large part of the outpost may be temporarily formed of cavalry.