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 increase the accuracy of German artillery-fire as the British attacked. On 23 September, Crown Prince Rupprecht wrote in his diary that the higher ground at Zonnebeke and Gheluvelt was vulnerable to another British attack and that it was vital that the German counter-attack tactic did not fail again. Next day, Rupprecht wrote that he hoped that another British attack would be delayed, as the 4th Army had insufficient reserves for the whole of the active front east of Ypres. Rupprecht ordered a (methodical counter-attack) against the British flank between the Menin Road and Polygon Wood, which was longer after the