The Battle of Loos was the largest British battle that took place in 1915 on the Western Front during World War I. It was the first time the British used poison gas and the first mass engagement of New Army units. The British battle was part of the attempt by the Allies to break through the German defences in Artois and Champagne and restore a war of movement. Despite improved methods, more ammunition and better equipment, the Franco-British attacks were contained by the German armies, except for local losses of ground. British casualties at Loos were about twice as high as German casualties.