The turrets were protected with an armour thickness of on the face and 76 mm on the roof. The casemate armour was thick and that of the barbettes was 299 mm thick rather than the originally planned 305 mm.  "Hyūga", named after Hyūga Province, one of the traditional provinces of Japan, was laid down at the Mitsubishi Heavy Industries shipyard in Nagasaki on 6May 1915 and launched on 27 January 1917. Captain Shigeushi Nakagawa assumed command on 30 April and the ship was completed on that same day, too late for service in World War I. "Hyūga" was then assigned to the 1st Battleship Division of the 1st Fleet. Captain Kinzaburo Mimura relieved Nakegawa on 10 November. An explosion in No.3 gun turret killed 11 crewmen and wounded another 25 during a gunnery exercise on 24 October 1919. Mimura was relieved in his turn by Captain Genjiro Katsuki on 20 November. "Hyūga" accidentally collided with and sank the schooner "Hiromiya Maru", killing two of the sailing ship's crew, on 21 July 1920. On 29 August, the ship began the first of numerous patrols off the Siberian coast and in northern waters in support of Japan's Siberian Intervention against the Bolshevik Red Army. Captain Hidesaburo Ishikawa replaced Katsuki on 20 November and he was replaced by Captain Genji Ide on 20 November 1921. The ship aided survivors of the 1923 Great Kantō earthquake in September 1923. From the early 1920s through the late 1930s, "Hyūga" often cruised off the coast of China. Little detailed information is available about her activities during the 1920s. The ship was overhauled in 1927–1928, during which her forward superstructure was enlarged and her aviation facilities improved. Beginning on 27 March 1932, she patrolled off the coast of China after the First Shanghai Incident, together with her sister ship and the battlecruisers and . Beginning on 24 October 1934, "Hyūga" was drydocked at Kure Naval Arsenal and underwent an extensive reconstruction and modernisation that lasted until 7September 1936. During the Second Sino-Japanese War, the ship ferried two battalions of the 3rd Sasebo Special Naval Landing Force to Port Arthur, China, on 19 August 1937. She began the first of her patrols off the southern Chinese coast on 15 September that lasted until early 1941. On 30 June 1940 "Hyūga" served as the flagship for the Emperor of Manchuoko, Henry Pu-yi, during his state visit to Japan.