 He was promoted to vice-admiral on 5 September 1903.As an engineer, he also developed the "Ijūin Fuse," making use of the newly developed Shimose powder, which was successfully used in heavy naval artillery shells during Russo-Japanese War (1904–05).Ijūin became Vice-Chief of the Navy General Staff during the Russo-Japanese War, successively assumed the positions of commander-in-chief of the IJN 2nd Fleet, the IJN 1st Fleet, the Combined Fleet, and then became Chief of the Imperial Japanese Navy General Staff (1909–14).