For his services Ōyama received the title of marquis under the "kazoku" peerage system, and, three years later in January 1898, he became a field-marshal. In the Russo-Japanese War of 1904–1905 he was appointed the Commander-in-Chief of the Japanese armies in Manchuria. As Supreme Commander of the Japanese Manchurian Army, Ōyama had complete authority over all Japanese land operations during the war, and personally directed the tactics of Japanese forces in all major battles, winning the Battle of Liaoyang and repulsing Russian counter-attacks at the Battle of Shaho and the Battle of Sandepu. He was replaced by General Kodama Gentarō briefly during early 1905 due to illness, but recovered to direct Japanese forces in the final Battle of Mukden.