Starting in three days before the attack, these guns began firing as steadily as they could without overheating. Very often in our front _abri_ it was impossible to write because of the vibration. One day, when we stopped in the woods to change a punctured tire, the car was knocked off the jack by the shocks several times before we could remove the tire, and at last we had to run in on the rim. Finally, just before the men were to go over the top, the barrage was set down in front of the trenches and the men climbed over the parapet, and started walking towards the enemy. It is always possible to tell the _tir de barrage_ by the sound of the guns. There is a certain regularity which is lacking when each gun is firing at independent targets, and the steady thunder gives one the feeling of a tremendous hammer smashing, smashing, irresistibly, each blow falling true and hard, and following one another with the regularity of the machines in a giant factory. A perfect barrage is impenetrable, with the shells falling so near together and with such short intervals of time between that nothing can survive it. The only possibility is the inaccuracy of some one or more guns which will put a number of shells out of the line and leave a break or opening. Before the attack the officers all have their watches carefully synchronized, as a mistake of one minute may cost many lives. Walking ahead of their men, keeping them the right distance behind the solid wall of flame and steel, they wait until a certain minute when the barrage is lifted a number of yards and then advance to that distance. In the orders, the minute the barrage is to be lifted and the distance are given out beforehand; for to advance the soldiers too quickly would be to put them under fire from their own guns. In this attack the first wave passed over the destroyed wire, and on reaching the enemy’s front-line trenches could not distinguish them from the rest of the ground, and found no living thing there. The second-line trenches were little better, and they got their fighting at the third-line trenches. So perfect had the preparation and execution of this attack been that the Bois d’A—— was cleared of the enemy in thirteen minutes from the time the French left their trenches. The first wave is followed by the “butchers” (the English “moppers-up”), who kill all the wounded and the odd prisoners, it being impractical for a charging line to attempt to hold a few captives. Also another factor which makes this treatment of prisoners necessary, and which the Allies have learned by experience, is that unguarded men, once the first wave has passed over them, will take out a machine gun and catch the advancing troops between two fires. This happened a number of times before the simple expedient was adopted of requesting the prisoners to go down into an _abri_ where they would be “safer,” and then tossing in two or three grenades which kill and bury them at the same time.