The new battle-ground was the area on both sides of the river Lys, between the La Bassée Canal and the Wytschaete Ridge. The German Staff knew that our front line had already been thinned to supply ten divisions for the struggle in the south, and at the moment it was weakly held, mainly by troops exhausted in the Somme battle. The enemy Staff chose their ground well. They had the great city of Lille behind them to screen the assembly. Certain key-points, such as Béthune and Hazebrouck, lay at no great distance behind the British front. The British communications were poor, while the German were all but perfect. If the enemy could break through at once between La Bassée and Armentières and capture Béthune, he could swing north-westward and take Hazebrouck and the hills beyond Bailleul, and so threaten the Channel Ports, on which the British armies depended for supplies.
The attack began on Tuesday, 9th April. A Portuguese division south of the Lys was driven in at the first thrust, and through the gap the enemy streamed in. At a quarter-past ten that morning he was more than a mile to the rear of the division holding the left of the gap, which was accordingly compelled to retreat. On the right of the gap, covering Béthune, lay the 55th West Lancashire Division. The story of the Lys is a story of the successful defence of key-points against critical odds, and Givenchy, where the men of West Lancashire stood, was most vital, for unless it fell Béthune could not be taken, and unless Béthune were captured at once the enemy attack would be cramped into too narrow a gate. The 55th Division did not yield though outnumbered by four to one. They moved back their left flank but they still covered Béthune, and their right at Givenchy stood like a rock. By noon the enemy was in the ruins of Givenchy; in the afternoon the Lancashire men had recovered them; in the evening they were again lost, and in the night retaken. This splendid defence was the deciding event in the first stage of the battle. It was due, said the official report, "in great measure to the courage and determination displayed by our advance posts. Among the many gallant deeds recorded of them, one instance is known of a machine-gun which was kept in action although the German infantry had entered the rear compartment of the pill-box from which it was firing, the gun team holding up the enemy by revolver fire from the inner compartment."