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. Artillery is useful to outposts when its fire can sweep defiles or large open spaces and when it commands positions that might be occupied by hostile artillery. The guns are carefully concealed or protected and are usually withdrawn at night. Machine guns are useful to command approaches and check sudden advances of the enemy. The field trains of troops on outpost duty generally join their organizations; if an engagement is probable, they may be held in rear. DISTRIBUTION OF OUTPOST TROOPS The outpost will generally be divided into four parts. These, in order from the main body, are the reserve, the line of supports, the line of outguards, and the advance cavalry. [Illustration: PLATE SHOWING THE IDEAS INVOLVED IN AN OUTPOST] The distance separating these parts, and their distance from the main body, will depend upon the object sought, the nature of the terrain, and the size of the command. There can be no uniformity in the distance between supports and reserve, nor between outguards and supports, even in the same outpost. The avenues of approach and the important features of the terrain will largely control their exact positions. The outpost of a small force should ordinarily hold the enemy beyond effective rifle range of the main body until the latter can deploy. For the same purpose the outpost of a large force should hold the enemy beyond the artillery range. The reserve constitutes the main body of the outpost and is held at some central point from which it can readily support the troops in front or hold a rallying position on which they may retire. The reserve may be omitted when the outpost consists of less than two companies. The reserve may comprise one-fourth to two-thirds of the strength of the outpost. The supports constitute a line of resisting and supporting detachments, varying in size from a half company to a battalion. They furnish the line of outguards. The supports are numbered consecutively from right to left. They are placed at the more important points on the outpost line, usually in the line on which resistance is to be made in case of attack.