British war crimes September 1915 and continued their usage for the remainder of the war. This was done in retaliation for the use of chlorine by Imperial German Army the preceding April. Following the Imperial German Army's use of poison gas at Ypres, the commander of II Corps, Lieutenant General Sir Charles Ferguson, had said of poison gas: Mustard gas was first used effectively in World War I by the German army against British and Canadian soldiers near Ypres, Belgium, in 1917 and later also against the French Second Army. The name "Yperite" comes from its usage by the German army near the
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