DEFENSIVE ENGAGEMENTS. When the troops have to withstand an attack on their lines, they must bear in mind the very sound principle of war that a passive resistance can only end in defeat. On the first lines all the elements necessary for as long a resistance as possible will have to be accumulated. The infantry will then have occasion to make a telling use of rifles, grenades, rifle machine-guns, and machine-guns in as great a number as possible. The supporting troops and the reserves must be ready to counter-attack the enemy without loss of time, and throw him out of any trenches he may occupy temporarily. We have often seen German attacks on advanced trenches repulsed in the very moment of success by a simple bayonet charge made by the troops of the first lines. To the field artillery, however, belongs the most important rôle in repulsing the attacks of the enemy, and the “communiqués” of all the Allies show that eight out of every ten attacks are repulsed by barrage fire. When the aviators can report in time exactly where the enemy troops are being massed for attack, the trench artillery can work great havoc in the ranks of those usually compact formations. [Illustration: View taken about 10 A.M. during the attack of May 5, 1917] PROLONGED ENGAGEMENTS. What we have just said refers to attacks made from regularly organized lines which have not been entirely destroyed by shell-fire. On a ground where fighting has been proceeding continuously, the trenches are entirely destroyed, and the men and machine-guns belonging to the first-line troops remain with no other shelter than shell-craters, which are, as far as possible, connected together during the night by shallow trenches, provided this work is not prevented by continuous shell-fire. The communication trenches with the rear do not exist any more; and connections can only be maintained with the utmost difficulty; by what means, we will later explain. In order to resume the attack under such conditions, it will be necessary to choose the exact moment when the enemy is supposed to be demoralized by the artillery, and to rush the troops forward. In nearly every case, the assistance of fresh troops or of troops that have suffered little will be needed. These field operations are difficult and require from both the chiefs and the soldiers a resolute will to conquer, and a thorough knowledge of war conditions.