If the hostile assault on the first line is successful, the fight for the occupation of the position, which takes place in the interior, has only begun. Opposing his frontal progression through the position, the enemy will encounter, as we know, a series of defensive lines disposed in depth. Also, for instance, if a nest of resistance holds up the progress of a part of the assaulting troops, the successive overlapping waves will carry on along the flanks of this stronghold. If, then, the position is strongly divided into compartments, the fire of such defenses will take these overlapping troops in the flank and rout them. The defenders may also play an active rôle and the enemy is likely to encounter new troops sent up for the purpose of counterattack. The division of the ground in support points, centers of resistance and sectors, has precisely for its object the localization of the enemy’s attacks. Each area must be organized to defend itself, independently of any other part of the position. Consequently, the officers must explain this condition to their men, so that they will have no concern if they see that the enemy has penetrated and is attacking them on the flank or rear. On the other hand, if several of these compartments hold their ground, the enemy may find himself surrounded in a certain area and cut off from the rear by barrage fire. Thus abandoned in a part of the position that he has momentarily taken, a vigorous counterattack will drive him out. =Defense of an Area.= The defense of each area is made similarly to that of the first line, as these areas embrace the successive lines of the position. The areas range in importance from front to rear, the support point embracing the first line, the center of resistance the first two lines, and the sector all three lines of the position. The alarm of an attack is relayed by the area commanders, the captain to the battalion commander, who in turn communicates it to the colonel of the sector. Not only the attacked portion of the sector is affected by this alarm, but the whole sector, so to speak, takes up arms. Let us see what happens as a result of this. All defenders of the area who have a special duty, immediately occupy their posts and remain there awaiting developments of the attack. For example, telephone men will remain at their instruments, runners will repair to their relay posts, observers occupy their observatories, and chiefs and headquarters officers remain at their command posts. And above all, the machine gun crews will man the guns disposed for interior fighting. [Illustration: FUNCTION OF COUNTER ATTACKS IN INTERIOR OF THE POSITION]