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
Actions of 30 September – 4 October 1917 the counter-attack. After the attack of 26 September, the British had used information from prisoners, gleanings from the battlefield and ground observation to judge the state of the 4th Army. The concentration of the German heavy artillery into the Tenbrielen, Kruiseecke, Becelaere and Keiberg groups directed towards Menin Road Ridge, Tower Hamlets Ridge, Polygon Wood and Broodseinde Ridge was reported on 29 September by I Anzac Corps flash spotters; RFC reconnaissance flights confirmed the changes but this took from 1 to 2 October, because Germans hid the redeployment with smoke screens. By 29 September, the 4th Army had recovered from