In 1915, he took command of the Army of the Bug and was concurrently commander of Heeresgruppe Linsingen. In June 1916, his Army Group faced the Brusilov offensive. After an initial retreat, he checked the Russian advance at the Battle of Kowel. He was promoted to Colonel-General, the second highest rank for a general in the Imperial German Army (4 stars). In 1917-1918 and especially after the signing of the Treaty of Brest-Litovsk, he led the German advance into the Ukraine.