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 removing more guns from the Third Army and Fourth Army, which were further south in Artois and Picardy. The increased amount of heavy artillery was to be used to destroy German concrete shelters and machine-gun nests, which were more numerous in the German battle zones, than the outpost zones which had been captured in July and August and to engage in more counter-battery fire. Few German concrete pill-boxes and machine gun nests had been destroyed during earlier preparatory bombardments and attempts at precision bombardment before attacks had also failed. The and guns and howitzers in the Second Army on 31