 He became a close confidant of navy chief Admiral Yamamoto Gonnohyoe, and was an important planner and specialist in naval technology.Promoted to rear admiral on 26 September 1899, Ijūin was a strong proponent of better relations between Japan and the United Kingdom, and worked to develop the Anglo-Japanese Alliance (1902) from behind the scenes.He was on a diplomatic mission to the United Kingdom in 1902 with Major-General Fukushima Yasumasa, and was awarded an honorary Knight Commander of the Order of the Bath (KCB).