The German offensive at Verdun forced the French to concentrate all their available strength on that sector of the line, thus leaving the British to cover the sectors left vulnerable by the removal of French troops and artillery. At Vimy Ridge, a labyrinth of tunnels -some prewar- already existed, and throughout April and May British tunnellers gradually improved their position; the Germans, seeing their advantage slip from their grasp, prepared once more to go into the attack.

This article is located in the History of the First World War Volume 4 (REF D522 .H58 1969 V.4).