ADVANCE GUARDS. The principal de tachment insuring security for the command in the field, which covers the head and flanks of a column or army advancing in the direction of the enemy. For a large force the advance guard is necessarily composed of troops of all arms; its strength being proportioned to that of the main force; the more or less resistance of an independent character it may be required to make; and the greater or less extent it may be found necessary to embrace by its advanced posts on the front and flanks to watch and an ticipate every movement of the enemy. The proportion of the advance guard to the main body may vary from a third to a fifth of the total force. In armies of some strength, or large corps d'ormie, particularly where the nature of the country requires a wide develop ment of advanced posts, the larger proportion is demanded; as at least one-third or even one half of its strength will be required for the advanced post service. In a small force of two or three thousand men one-fifth will usually be all that can be well spared for the same purposes. The purpose in all cases should be to keep the enemy in a state of uncertainty and even to act offensively against him when occasion offers so as to keep him in doubt as to the actual character and numbers of troops before him. In all defective positions the advance guard and its advanced posts should retire slowly, but circumspectly, so that the main body may have time to take all its de fensive measures. In the offensive the attack of the advance guard should be decided and vigorous; pressing upon the enemy at every point ; and leaving nothing undone to demoral ize him by the confusion which so often fol lows from an impetuous onset. In all affairs of advance guards great circumspection is to be shown both by the officer in command of the advance guard in throwing forward fresh troops to strengthen a point assailed, as well as on the part of the general-in-chief in sustain ing the advance guard by weakening his main body. These are points that can only be de cided on the spot. The safer rule in all cases is not to weaken the main defense, or main attack, by detaching from it to support a feeble point. If the force engaged under such
circumstances does not suffice for its own de fense it is best for it to fall back in time and, taking position with the main body, endeavor, by their combined efforts, to turn the scales of victory in their favor.
The strength of an advance guard depends upon: (1) The force it is cov ering. (2) The object for which it is organ ized. If its commander is instructed to engage the enemy whenever found, its strength should be at least one-fourth of the entire command. If, however, he is only to delay the enemy's ad vance to give the main body time to deploy, it should be as small as is consistent with this duty—for a large force, from one-sixth to one-eighth will suffice. (3) On the nature of the country. (4) The character of the enemy. (5) The distance it is required to precede the main body. Its strength should never exceed one-third of the command and rarely be dimin ished below one-sixth. The 'strength of ad vance guards would usually be as follows: One battalion of infantry (four companies), one-half to one company; One regiment of infantry (12 companies), two to three companies; One brigade of infantry (36 companies), six to 10 companies.
In an infantry division, approximately the following number of troops would be detailed on advance-guard duty: From the three brigades of infantry, two regiments; From the two regiments of artillery, one battalion; From the regiment of cavalry, two bat talions; From the one company of engineers, one half company of engineers.
One of the important duties of the army commander is to determine the strength and composition of his advance guard and he must hear in mind many things in addition to those already mentioned. (1) If the enemy is near the duty will he arduous. (2) That detach ments from the main body may impair its strength at a critical moment. (3) That an ambitious officer, finding himself in command of a strong force, may unwisely become in volved with a stronger one and thus force his chief to deploy the main body to extricate his advance guard. He must also remember that the defensive powers of small bodies have been increased by improvements in fire-arms.