The offensive at Ypres slackened to meet the Allied attacks elsewhere, and our troops in the salient at least were not insensible to the fact that even the Germans had insufficient artillery or high-explosive to maintain an intense bombardment all along the line. Both the French and ourselves began on 9 May, and the object was to threaten the German position in front of Lens and Lille. Lens was protected by a bulge in the German front which ran round by Grenay, Aix-Noulette, Notre Dame de Lorette, Ablain, and Carency to the north-west of Arras, and then south-eastwards by La Targette, Écurie, and Roclincourt. Between this line and Lens lay the Vimy Ridge, and in front of its southwestern slopes the Germans had constructed elaborate fortifications above and underground known as the White Work and the Labyrinth. For the attack the French had made careful preparations, and their concentration of eleven hundred guns and almost limitless shells exceeded in intensity any previous experiment. They were rewarded by the comparative ease with which their initial successes were secured. Barbed wire and earthen parapets were blown to pieces before the infantry attacked and in an hour and a half coveted two and a half miles. La Targette and the White Work were captured and an entrance forced into Neuville St. Vaast. Farther north a second attack was required, and it was not until the 12th that Carency, Ablain, and the summit of Notre Dame were mastered. The line had been broken, but the fragments resolved themselves into almost impregnable strongholds; it took another fortnight before the Souchez sugar-refinery, half a mile in front of Ablain, fell, and the Labyrinth held out, while behind these defences rose the Vimy Ridge to defy for another two years all attacks upon Lens (see Maps, pp. 79, 302).