Chemical weapons and the United Kingdom army against British and Canadian soldiers near Ypres, Belgium, in 1917 and later also against the French Second Army. The name Yprite comes from its usage by the German army near the town of Ypres. The Allies did not use mustard gas until November 1917 at Cambrai, France, after the armies had captured a stockpile of German mustard-gas shells. It took the British more than a year to develop their own mustard gas weapon, with production of the chemicals centred on Avonmouth Docks. (The only option available to the British was the Despretz–Niemann–Guthrie process). This was used first in September
Action of 25 September 1917 defeat German counter-attacks, by advancing no more than and then consolidating their positions, preferably on reverse-slopes. When the Germans counter-attacked, they would encounter a British defence-in-depth protected by artillery and suffer many casualties to little effect, rather than the small and disorganised groups of infantry that the Germans had driven back on 31 July, After the big defeat at the Battle of the Menin Road Ridge on 20 September, the 4th Army changed the organisation of regiments and battalions in their defensive positions. During August, each German front-line division had kept two regiments in the front position, with all six