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
Battle of Arras (1917) the Western Front, in Operation Alberich. By the spring of 1917, the German army in the west had a strategic reserve of "Experience of the German 1st Army in the Somme Battles", ("Erfahrungen der I Armee in der Sommeschlacht") was published on 30 January 1917 by Ludendorff but new defensive methods were controversial. During the Battle of the Somme in 1916 Colonel Fritz von Loßberg (Chief of Staff of the 1st Army) had been able to establish a line of "relief" divisions (), with the reinforcements from Verdun, which began to arrive in greater numbers in September. In his analysis