The front held by the Canadian Corps on April 8, 1918, was approximately 16,000 yards in length. It will be remembered that the Second Canadian Division under the Sixth Corps (Third Army) was holding 6,000 yards of front, making a total of 22,000 yards of front held by Canadian troops. On April 9, 1918, the Germans attacked on the Lys front between La Bassée and Armentières. Making rapid progress, they crossed the Lys River on the 10th, and on the following days advanced west of Merville-Bailleul. They were well held at Givenchy by the Fifty-fifth Division and their attack made no progress southward. The Canadian Corps was not involved in this fighting, but it now found itself in a deep salient, following with anxiety the development of the Battle of the Lys. The Battle of the Lys added a new burden to the already sorely tried British Army, and it was imperative that troops should at once be made available to stop the German advance. On the 10th, the Canadian front was extended by taking over from the First Corps the line held by the Forty-sixth Division (Lens-St.-Emile-Hill 70 sector). This relief was commenced on April 11, 1918, and completed on the night of the 12th-13th by the Third Canadian Division; concurrently with it, the inter-divisional boundaries were readjusted and the artillery redistributed to meet as well as possible the new conditions. The front held by the three divisions then in the Canadian Corps had a length of approximately 29,000 yards, and of necessity the line was held very thinly and without much depth. To deceive the enemy regarding their dispositions and intentions, the Canadians adopted a very aggressive attitude. The artillery constantly harassed the enemy's forward and rear areas and the infantry penetrated his line at many points with strong fighting patrols and bold raiding parties. Gas was also projected on numerous occasions. This activity on the immediate flank of the Lys salient greatly perturbed the enemy, who gave many indications of nervous uncertainty. The situation was critical, and extensive steps were taken at once to increase the ability of the Canadian Corps to withstand hostile attacks. The success of the German offensive emphasized the need of greater depth for defensive dispositions, which depend very largely on the stopping power of the machine gun. Unfortunately the number of machine guns with a division was inadequate to give the required depth of defense on a front exceeding 4,000 yards in length. Each Canadian division was now holding a front approximately 10,000 yards in length, and the extemporized machine-gun detachments formed previously, added to the machine-gun companies of the Fifth Canadian Division, were far from sufficient for the task.