Chemical weapons in World War I volatile oily liquid. It was introduced as a vesicant by Germany in July 1917 prior to the Third Battle of Ypres. The Germans marked their shells yellow for mustard gas and green for chlorine and phosgene; hence they called the new gas "Yellow Cross". It was known to the British as "HS" ("Hun Stuff"), and the French called it "Yperite" (named after Ypres). Mustard gas is not an effective killing agent (though in high enough doses it is fatal) but can be used to harass and disable the enemy and pollute the battlefield. Delivered in artillery shells, mustard gas was
Action of 22 October 1917 Action of 22 October 1917 The Action of 22 October 1917 was an attack during the Third Battle of Ypres in the First World War by the British Fifth Army and the French First Army against the German 4th Army. British attacks had been repulsed at Passchendaele by the 4th Army at the Battle of Poelcappelle (9 October) and the First Battle of Passchendaele (12 October). While the British waited for another dry spell and the completion of plank roads up to the new front line, the Canadian Corps and fresh British divisions were transferred to Flanders by the British