All over this lower slope of the Vimy Ridge is a litter of enormous destruction caused by our gun-fire. German guns and limbers, machine-guns and trench-mortars lie in fragments and in heaps in infernal chaos of earth, which is the graveyard of many German dead. The first hint that the Germans were in retreat from Liévin, near Lens, was given by the strange adventure of two of our airmen. They had to make a forced landing near Lens, and one of them was wounded in the leg. Our observing officers watching through glasses expected them to be made prisoners, but they were seen afterwards smoking cigarettes and slapping themselves to keep warm. It now turns out that the German soldiers did not wait to take them, and finding one man wounded left the other to look after him. The next sign that the enemy was about to go was when the fires and explosions went up in Liévin and Lens, and when he began to shell his own front lines outside those places. All through the night the sky was aflame with these fires, and this morning I saw that the enemy was making a merry little hell in Lens and all its suburbs and dependent villages. I had no need to guess the reason of all this. On the way I had met two young Alsatian prisoners just captured. They had been left with orders and charges to blow up mine-shafts, but had been caught before they had done so. They had no heart in the job anyhow, being of Alsace, and with their comrades had already petitioned to fight on the Eastern instead of the Western Front. They described the panic that reigned in Lens, and the fearful haste to destroy and get away. For hours to-day I watched that destruction while our troops were working forward through Liévin to get the better of the nests of machine-gun redoubts at the entrance to Lens, from which intense fire still came.