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
Mines in the Battle of Messines (1917) Second Army (General Sir Herbert Plumer), remarked to the press, "Gentlemen, I don’t know whether we are going to make history tomorrow, but at any rate we shall change geography". The Battle of Messines marked the zenith of mine warfare. On 10 August 1917, the Royal Engineers fired the last British deep mine of the war, at Givenchy-en-Gohelle near Arras. As part of allied operations in the Ypres Salient, British mining against the German-held salient at Wijtschate near Messines had begun in spring 1915, with diggings below the surface. The concept of a deep mining offensive was devised in September