When World War I began, Duke Albrecht's VI Inspectorate Corps was formed into the 4th Army, 123 battalions strong. As King William II had no sons, Albrecht was appointed the army's commander and assigned to the Ardennes, with Walther von Lüttwitz serving as his Chief of Staff. This army he led to victory alongside Crown Prince Wilhelm's 5th Army at the Battle of the Ardennes in August 1914. Following that victory, the 4th Army saw action in the First Battle of the Marne before being transferred to Flanders in October, where Albrecht commanded them during the Battle of the Yser. Albrecht also commanded the German forces during the Second Battle of Ypres, where poison gas was used on a large scale for the first time.