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 diary note that it had been an awful experience; he did not know what to do against the British. Erich Ludendorff the (Quartermaster-General of the German Army, equivalent to the British Chief of the General Staff) conferred on 29 September with (field marshal) Crown Prince Rupprecht the commander and (lieutenant-general) Hermann von Kuhl the chief of staff, of "Heeresgruppe Kronprinz Rupprecht von Bayern" (Army Group Rupprecht of Bavaria), the 4th Army commander, General Sixt von Armin and the 4th Army chief of staff, (major-general) Fritz von Loßberg. The staff officers of the 4th Army (corps headquarters) agreed that defensive manoeuvres