Yūbari (夕張) was an experimental light cruiser built during the early 1920s for the Imperial Japanese Navy (IJN) to test new concepts for reducing the hull's weight while strengthening it.

During the war Yūbari was the flagship of the forces involved in the Battle of Wake Island and was then sent south to support the invasion of Rabaul in early 1942.

She played a small role during the Battle of the Coral Sea as the flagship of the forces intended to invade Port Moresby, New Guinea.

Yūbari spent the rest of the year on escort duties and she played a small role in the Battle of New Georgia in mid-1943 as she bombarded Allied forces a few days after they landed on the island.

Hiraga believed that this would allow him to design a ship that would have the combat potential of the standard 5,500-long-ton (5,588 t) Sendai class light cruiser, but with a much lighter displacement.

Lieutenant Commander Kikuo Fujimoto designed Yūbari, under the direction of Hiraga, to have nearly the same speed, armament and radius of action as the Sendais while displacing less than 60% of the older ships.

[2] Yūbari's propulsion system was derived from that of the Minekaze-class destroyers, enlarged by one additional propeller shaft, steam turbine and four Kampon water-tube boilers.

[2] In 1924, the funnel was raised by 2 meters (6 ft 7 in) to further reduce the amount of exhaust gases reaching the bridge and fire-control director at high speed.

The following year, Yūbari's mine storage equipment was removed, her hull girders reinforced and ballast installed during a refit from 17 May to 20 July 1934 after the top-heavy Japanese torpedo boat Tomozuru capsized during a storm.

[7] Shortly after the start of the Pacific War, Yūbari had a pair of improvised twin-gun mounts for 13.2 mm machine guns installed on either side of her bridge.

Completed just prior to the 1923 Great Kantō earthquake on 1 September, Yūbari was quickly pressed into service to help evacuate refugees from the Shinagawa area.

[11] Yūbari made a lengthy cruise during April–June 1925 in the Western Pacific, including a visit to Australia, and observed the fleet exercises of the United States Navy west of the Hawaiian Islands.

The squadron escorted troopships carrying Imperial Japanese Army troops past Chinese forts at the mouth of the Huangpu River in Wusong on 8 February.

Afterwards, she was assigned to the 5th Destroyer Squadron of the 3rd Fleet and conducted patrols off of the China coast and visiting the island of Java in the Dutch East Indies in 1936.

With the start of the Second Sino-Japanese War in August 1937, Yūbari assisted in the evacuation of Japanese civilians from coastal cities in southern China.

On 14 September Yūbari and the destroyers Hayate and Oite were entering the Pearl River Delta at Bocca Tigris when they encountered the elderly protected cruiser Chao Ho and the sloop Hai Chow (formerly the Arabis class HMS Pentstemon).

On 15 November Yūbari became flagship of the 6th Destroyer Squadron, commanded by Rear Admiral Sadamichi Kajioka, of the 4th Fleet, tasked with the defense of the South Seas Mandate.

She was briefly refitted at Yokohama 20 April–1 May and departed Japan for a tour of the Mandated Islands on 25 May that lasted until she began training at Truk on 25 October.

Kajioka's ships began bombarding the shore with little effect on the morning of 11 December, but the island's USMC defenders sank two destroyers, damaged two others as well as a light cruiser, forcing Kajoika to withdraw to Kwajalein.

[15] While preparing for subsequent operations, Yūbari's anti-aircraft suite was reinforced by two pairs of Type 93 machine guns, one on each side of the bridge on 3 January 1942.

The 6th Destroyer Squadron then spent the next several months escorting the forces involved in the capture of Rabaul and Kavieng, New Ireland, off the coast of New Guinea on 23–24 January, followed by the Invasion of Salamaua–Lae on 8 March.

On 10 March, she was attacked by two Douglas SBD-3 Dauntless dive bombers from the Lexington, which scored two near-misses that killed a number of her anti-aircraft gun crews.

[16] Beginning on 29 June 1942, Yūbari took part in the Solomon Islands campaign, including landing personnel on Guadalcanal to construct an airfield.

She was transferred to Rabaul on 17 July and began to develop problems with her center turbine around that time that limited her to 26 knots (48 km/h; 30 mph) on two shafts.

[18] Yūbari escorted the landing force for Operation RY, the occupation of Nauru and Ocean Islands, departing Truk on 26 August and returned there on 5 September.

On her return to Buin, Yūbari struck a naval mine laid by a Grumman TBM Avenger torpedo bomber, it damaged her bow, limited her speed to 22 knots (41 km/h; 25 mph) and wounded 26 crewmen.

On 6 November, she undertook a "Tokyo Express" transport run with 700 troops from the IJA 17th Division and 25 tons of supplies to Bougainville Island.

On 18 November, she attempted another troop transport run to Garove Island in New Britain, but the mission was cancelled after Yūbari was damaged in an attack by USAAF B-24 Liberators and USN PBY Catalinas.