British war crimes September 1915 and continued their usage for the remainder of the war. This was done in retaliation for the use of chlorine by Imperial German Army the preceding April. Following the Imperial German Army's use of poison gas at Ypres, the commander of II Corps, Lieutenant General Sir Charles Ferguson, had said of poison gas: Mustard gas was first used effectively in World War I by the German army against British and Canadian soldiers near Ypres, Belgium, in 1917 and later also against the French Second Army. The name "Yperite" comes from its usage by the German army near the
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