Then north of the great salient just occupied, the Germans struck, on
April 9, between the important British depots of Arras and Ypres, forty
miles apart, concentrating on a twelve-mile front between Givenchy and
Fleurbaix. During the two following days the concentration moved north
five miles, penetrating between Armentières and Messines. On the 11th it
had developed as far north as Hollebeke, four miles southeast of Ypres,
had partly enveloped Messines Ridge and entirely Armentières and the
town of Estaires on the Lys River. By the 12th it had swelled beyond
Merville and Lestrem in the south, was threatening the railway junction
of Bailleul in the middle ground, had gained a footing on Messines
Ridge, and was investing the neighboring heights of Neuve Eglise and
Kemmel in the north. By the morning of the 17th the German penetration
had reached Locon in the south, the Nieppe Forest in the middle ground,
and had occupied Bailleul and the eastern heights of the ridge in the
north and threatened the western and more elevated heights of Mont Rouge
and Mont Kemmel. Thus in eight days the Germans had developed a sector
on the Lille front of originally twenty-two miles, a salient embracing
an area of about 825 square miles with a new front of about thirty-five
miles.