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
6th Army (German Empire) eventually come to be regarded as one of Germany's most able generals. On 24 September 1915 the 6th Army was the target for the British Army's first chlorine gas attack of the war. Despite the horrific casualties inflicted, the British offensive became bogged down after several days. Rupprecht was promoted to the rank of field marshal ("Generalfeldmarschall") in July 1916 and assumed command of Army Group Rupprecht on 28 August that year, consisting of the 1st, 2nd, 6th and 7th Armies. Following Rupprecht's promotion, command of the 6th Army was given to General Ludwig von Falkenhausen. In March 1917 the