Sir Julian Byng, to whom these operations were entrusted, received instructions to dispense with artillery preparation, and to depend entirely on the tanks, to cut through the enemy’s wire. This was an entirely new departure. Hitherto it had been generally admitted by both sides that no infantry attack could possibly succeed, without an artillery preparation and a creeping barrage, and it remained to be seen whether the absence of all artillery support would be compensated for by the tanks, and by the undoubted advantage of attacking without giving the enemy any warning. With the utmost secrecy Sir Julian Byng assembled flotillas of tanks, and hid them in the woods. The attack started on November 20, and succeeded beyond all expectations, for not only was the Siegfried line pierced to a depth of six miles, but over 10,000 prisoners and 142 guns were taken. The capture of Bourlon Wood was successfully effected, but the Germans soon recovered from their surprise, and commenced to bring up reinforcements, with the result that the Guards Division on attempting a farther advance on Fontaine found the enemy in great strength. The ground that had been gained during the British advance formed an awkward salient about ten miles in width and six miles in depth, and the problem that confronted Sir Douglas Haig was whether to continue the advance or to withdraw. After weighing the various considerations involved, he came to the conclusion that it would be best to advance. On the enemy’s side the Germans were at first rather staggered at finding that their impenetrable Siegfried line had been pierced, but Ludendorff determined to take advantage of the situation that had been created, and to strike on each side of the salient with a view to cutting off the troops in front.