Sulfur mustard later also against the French Second Army. The name Yperite comes from its usage by the German army near the town of Ypres. The Allies did not use mustard agent until November 1917 at Cambrai, France, after the armies had captured a stockpile of German mustard shells. It took the British more than a year to develop their own mustard agent 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 1918 during the breaking of the Hindenburg Line. Mustard agent was dispersed
Action of 25 September 1917 about the new conditions produced by German defence-in-depth. The 4th Army had spread strong points and pillboxes in the areas between its defensive lines and made rapid counter-attacks with local reserves and "Eingreif" divisions ("Eingreifdivisionen", specialist counter-attack divisions), against Allied penetrations. Plumer issued a preliminary order on 1 September, which defined the Second Army area of operations as Broodseinde and the area to the south. The plan was based on the use of much more medium and heavy artillery, which had been brought to the Gheluvelt Plateau from VIII Corps, on the right flank of the Second Army and by