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
Actions of 30 September – 4 October 1917 Actions of 30 September – 4 October 1917 The Actions of 30 September – 4 October 1917 were German methodical counter-attacks ("Gegenangriffe") during the Third Battle of Ypres in Flanders, during the First World War. Hasty counter-attacks () by the German 4th Army during the Battle of the Menin Road Ridge on 20 September and the Battle of Polygon Wood on 26 September, had been costly failures. On 29 September, a review was held at Roulers by Erich Ludendorff the (Quartermaster-General of the German Army, equivalent to the British Chief of the General Staff) with the commanders of "Heeresgruppe Kronprinz