In the organizational structure of the Imperial Japanese Navy in 1886, the Japanese Empire was divided into five operational districts, with the Hokkaidō-Ōshu area forming Naval District 5, with its nominal headquarters in Muroran, Hokkaidō. However, the area was given a low priority in funding, and remained largely a paper organization under overall command of the Yokosuka Naval District. On 12 June 1895, the nominal headquarters of Naval District 5 was transferred from Muroran to the more sheltered port of Ōminato with Mutsu Bay, although facilities and infrastructure were minimal. After the Russo-Japanese War, when the strategic importance of control of the Tsugaru Straits came into focus, and with Japan's acquisition of Karafuto Prefecture, more investment was made in securing Japan's northern frontiers. Ōminato was one of eleven designated third echelon naval ports, or yokobu located in various locations around Japan. In December 1905 it was made independent of Yokosuka. Although Muroran, Asahikawa and Wakkanai bases reported to Ōminato, it was not raised to full Naval District headquarters status, but continued as Ōminato yokobu. A wireless station was completed in 1913. On 9 October 1913, the Inazuma-class destroyer suffered from an explosion of her No. 3 boiler while at Ōminato. The incident highlighted the need for better facilities at Ōminato, and a ship repair facility and naval hospital were completed by 1923. On 19 July 1931, the ship repair facilities at Ōminato caught fire and were largely destroyed, and had to be rebuilt a year later. The Ōminato Naval Air Station was opened in November 1933. In September 1936, after the IJN 4th Fleet Incident, Ōminato received the destroyers and for emergency repairs. On 20 November 1941, Ōminato was finally raised to the status of a Guard District In concept, the Guard District was similar to the United States Navy Sea Frontiers concept. Each Guard District maintained a small garrison force of ships and Naval Land Forces which reported directly to the Guard District commander, and hosted detachments of the :Category:Fleets of the Imperial Japanese Navy|numbered fleets on a temporary assignment basis. After the start of the Pacific War, Ōminato became the home port of the IJN 5th Fleet. The attack on Dutch Harbor in the Aleutian Islands that occurred simultaneously with the Battle of Midway was launched from Ōminato. Ōminato was bombed several times in the closing days of the war: 14 July, 15 and 28 July, followed by a large attack from August 8–10, 1945, which destroyed several ships. American forces landed from the to accept the surrender of the base from the Imperial Japanese Navy on 9 September 1945. The base facilities were used by the United States Navy during the occupation of Japan until 16 September 1953. A portion of the former base is now in use by the Japan Maritime Self Defense Force as JMSDF Ōminato Base.
