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 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