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 the night. An intelligence summary of the Second Army assessed the German artillery in support of the of 25 September, to have been the greatest concentration of artillery on a German divisional sector ever known and was nearly four times the usual quantity for a division. The attacking battalions had assembled during the night of covered by parties of the line-holding battalions opposite the 33rd Division. The great mass of German artillery began a bombardment at but fell short and German infantry fired red flares to signal to the German artillery that they were falling short, especially on the III