DEFENSE OF A DEFILE.
215.—To keep the exits open for an advance.
If the aim is to keep the exits open so as to permit the advance of troops, the defense should be organized at some distance in front of the defile: far enough to permit the unimpeded progress of the advance.
216.—To keep exits open for a retreat.
If the aim is to keep the exits open so as to cover the retreat of troops, the roads at the bottom of the defile should be left free and the defense troops so placed as to draw the enemy's fire on other points.
217.—To block the defile.
If the aim is to block the defile, the defense should be organized in the interior of the defile on both sides of the place of greatest width, so as to secure convergence of fire. Echelon detachments all along the defile to act as a rear guard in case a retreat is necessary. Keep the flanks well protected.