[395.] In defense, reconnaissance must be kept up to determine the enemy's line of advance, to ascertain his dispositions, to prevent his reconnaissance, etc.
Patrols or parties posted to prevent hostile reconnaissance should relieve the main body of the necessity of betraying its position by firing on small bodies of the enemy.
[396.] Reconnaissance continues throughout the action.
A firing or skirmish line can take care of its front, but its flanks are especially vulnerable to modern firearms. The moral effect of flanking fire is as great as the physical effect. Hence, combat patrols to give warning or covering detachments to give security are indispensable on exposed flanks. This is equally true in attack or defense.
[397.] The fact that cavalry patrols are known to be posted in a certain direction does not relieve infantry commanders of the responsibility for reconnaissance and security.
To be surprised by an enemy at short range is an unpardonable offense.
[398.] The commander of a battalion on a flank of a general line invariably provides for the necessary reconnaissance and security on that flank unless higher authority has specifically ordered it. In any event, he sends out combat patrols as needed.
Where his battalion is on a flank of one section of the line and a considerable interval lies between his battalion and the next section, he makes similar provision.
[399.] Battalion commanders in the first line establish patrols to observe and report the progress or conduct of adjoining troops when these can not be seen.