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 were to be replaced by a policy of fighting for every piece of ground. Armin thought that even if counter-attacks failed to recapture ground, the British would keep more troops in the front line and that German infantry casualties were no worse in counter-attacks than under British barrages. On 30 September, the 4th Army issued an operation order for more field artillery bombardments between British attacks and that at least half of the heavy artillery ammunition was to be used for observed fire on captured pill-boxes, command posts and machine-gun nests, duckboard tracks and field railways. Gas bombardments were to