The Germans began the attack on the morning of April 9, after an intense bombardment with gas shells, and under cover of a dense fog reached the first machine-guns. The sector was held by Portuguese troops, wedged in between the British, from Bois-Grenier to Neuve-Chapelle.

On the whole length of front attacked, between La Bassée and Armentières, in the Plain of Flanders, the only natural obstacles are the rivers and canals. From the beginning of the battle the Portuguese were thrown into disorder by the extreme violence of the attack.

The twenty-one German shock divisions attacked in five columns: to the south, the first column in the direction of Givenchy; the second (General Kraevel), in front of Festubert; the third (Von Bernhardi) marched against La Couture and Richebourg-St.-Waast; the Carlowitz Corps, forming the fourth column, advanced against Estaires in the direction of Laventie; further north, the fifth column attacked in the direction of Fleurbaix, outflanking Bois Grenier and Armentières on the west.

Under the pressure of the attack, a depression was formed in the line. Fleurbaix, Laventie, Richebourg-St.-Waast and Neuve-Chapelle were lost, and the Germans reached the Lys between Estaires and the St. Maur Ferry. To the north of the pocket the Allies resisted successfully at Fleurbaix; to the south, Givenchy, after a desperate struggle, remained in the hands of the British.

On the following day the German troops, continuing the push towards the centre, succeeded in crossing the Lys between Estaires and the St. Maur Ferry.

The battle extended northwards and the IVth Army (Von Arnim) attacked between Armentières and Ploegsteert with the Eberhardt, Marschall and Sieger Corps.

The push continued on the 11th, and Armentières, outflanked on the north and south, smashed by the shells and drenched with gas, had to be evacuated.

On their left, the Germans, after crossing the Lawe, north of Locon, two miles from Béthune, captured Neuf-Berquin and Merville.

Givenchy, held by the British 55th Division, resisted all attacks and remained in their hands.

On the right, Nieppe and Steenwerk had to be evacuated. The German advance to the south of Armentières becoming more pronounced, the British straightened their front, to avoid too sharp a salient, and fell back to the Messines-Wytschaete Crest.