 In August 1941, just prior to Japan′s attack on European/US interests in the Pacific Theater, (some consider the 2nd Sino-Japanese war to be the real start of World War II), Ugaki was appointed Chief-of-Staff of the Combined Fleet under Admiral Isoroku Yamamoto in which he served until May 1943.He was promoted vice admiral on 1 November 1942.Traveling with Yamamoto in a separate Mitsubishi G4M bomber, both aircraft were shot down on 18 April 1943 over Bougainville in the Solomon Islands, in what the United States named "Operation Vengeance".