These minor local actions were the prelude to a powerful offensive which Field Marshal Haig was preparing, one of the greatest operations of the war, and which broke the famous Hindenburg line. The attack was launched on November 20, 1917, and was a complete surprise to the Germans as it had not been preceded by any artillery preparations. The operation was carried out by the third army under General Sir Julian Byng, the advance being made along a thirty-two-mile front between St. Quentin and the Scarpe River. German defenses were penetrated for a distance of five miles at the deepest point, extending to the village of Cantaing, which lies less than three miles to the southwest of Cambrai. As a substitute for the usual artillery preparation the British had secretly assembled a large number of tanks, which were sent forward under a screen of smoke, and broke down the German barbed-wire entanglements, opening the way for the infantry to make their forward rushes. The British troops were in high spirits, shouting and cheering as they pushed forward in the wake of the lumbering machines. As the tanks rolled on, showering machine-gun bullets before them, the British guns in the rear sent hurricanes of shells screaming over the Hindenburg line. The surprise of the attack seemed to have dazed and bewildered the Germans; many of them hid in their dugouts and tunnels and then surrendered. The braver element got their machine guns in action or used their rifles to snipe the British. The German artillery fire was feeble, their gun positions being smothered beneath the deluge of British shells. There were comparatively few batteries, and their infantry gained little help from them. It was well known to the British that they had removed many of their guns from this sector in the past few days, as this part of the battle line was considered "quiet." During the night preceding the attack the British had massed large bodies of cavalry very close to the enemy lines, ready for a sweeping drive when the tanks had broken down the wire defenses. In hollows near the German lines were thousands of cavalry horses with their horse artillery limbered up ready for the dash forward. After the tanks had made clear the way to advance the cavalry sprang forward through the rain and mist. One squadron rode down a battery of German guns, and other bodies swept around machine-gun emplacements and through villages and captured many prisoners.