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 September, German troops were to conduct a on the Fifth Army front opposite the 20th (Light) Division in XIV Corps and a bigger attack against the X Corps front, in the centre of the Second Army, south of the I Anzac Corps in Polygon Wood. The 50th Reserve Division had been the "Eingreif" division for from and was moved south to the Menin area as a reserve. The division relieved the Bavarian "Ersatz" Division on 21 September, Reserve Infantry Regiment 231 (RIR 231) south of the Menin road, RIR 230 north of the road to the Reutelbeek and RIR 229