Ōkuma Shigenobu
Katō became Minister of the Navy in August 1915, days before his promotion to full admiral on 28 August 1915. He served in this post in the cabinets of Ōkuma Shigenobu, Terauchi Masatake, Hara Takashi, and Takahashi Korekiyo. Under Hara and Takahashi, Katō was Japan's chief commissioner plenipotentiary to the Washington Naval Conference, and worked with Ambassador Shidehara Kijurō in the negotiations that led to the Five-Power Treaty.