The French continued active in the Verdun region, where they had to defend themselves from frequent counterattacks. In the Champagne territory French troops struck a shrewd blow on September 11, 1917, when in successful raids they drove across the German trenches between St. Hilaire and St. Souplet and penetrated the second line. Here there was intense and deadly fighting. The German defenders were either killed or made prisoners, and the French captured large quantities of supplies. North of Caurières Wood, northeast of Verdun, the French advanced line on a front of about 500 yards penetrated the German trenches and close fighting developed. This was the scene of continuous attacks and counterattacks for two days in which each side gained in turn a temporary ascendancy, but the result was indecisive. It was not until the night of September 14-15, 1917, that the French succeeded in ejecting the Germans from the greater part of the trench system here and took possession. In Champagne on September 14, 1917, a surprise attack made by the French in the region of Mont Haut was successfully carried out. A German observatory and a number of shelters and dugouts were destroyed and much damage wrought to the enemy defenses. No important operation was attempted by the British troops around Lens for several days following, but bombardments were incessant. The Canadians, though constantly under fire and subjected day and night to strong attacks, firmly held their positions. The situation of the Germans in the center of Lens with an active enemy occupying high ground to the north and south was not a comfortable one. When they did fight it was with rage and despair. Prisoners taken told of the deadly effects of the British gas projectiles which wrought awful havoc among the troops herded in tunnels and dugouts. The constant bombardment of Lens had reduced the city to the same ruined condition as the suburbs. The subterranean caverns which the Germans had built by the forced labor of civilians two years and more before became death traps. Often they collapsed under a heavy bombardment, burying alive whole companies in the ruins. Again, as frequently happened, a shell would explode inside the caves with fatal results to the occupants. The Germans had every reason to wish that they had never introduced poison gas in warfare, for as employed by the British it had become a far deadlier destructive weapon than in their own hands. Many times during these days the Canadians had flooded the city with gas which soaked down into the tunnels and dugouts and stifled men in their sleep, or they died with their masks on if they delayed a second too long.