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. Designs pioneered on Yūbari had a major impact on future Japanese warship designs. Completed in 1923, the ship was generally used as the flagship for destroyer squadrons. She spent large portions of her peacetime career in reserve or used as a training ship. The ship participated in the First Shanghai Incident in 1932 and the Second Sino-Japanese War in 1937 before World War II. 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. At the beginning of the Solomon Islands campaign, Yūbari escorted the forces that made the initial landings on the island of Guadalcanal in July. A few days after the Americans attacked the island in August, the ship participated in the Battle of Savo Island where she crippled an American heavy cruiser and a destroyer.
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. The ship stuck a mine on the return journey and had to return to Japan for repairs that lasted for several months. After her return to the Guadalcanal area in November, she made several Tokyo Express runs to deliver reinforcements and supplies. Yūbari was damaged by several American airstrikes at Rabaul later that month and had to return again to Japan for repairs that lasted until March 1944. The ship was tasked to deliver supplies and troops to Japanese outposts in April and was sunk by an American submarine later that month.
Background and description
Construction of an experimental light cruiser was authorized by the revised 1917 8-4 Fleet Program, but construction was not approved by the Naval General Staff until October 1921 to evaluate naval architect Captain Yuzuru Hiraga's innovative design proposal. He incorporated the ship's belt and deck armor plates as structural members into the hull structure, eliminating the weight of the traditional plating and structure that backed the armor. Hiraga believed that this would allow him to design a ship that would have the combat potential of the standard 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. Yūbari introduced numerous features that were adopted by subsequent heavy cruiser designs.
The cruiser was designed to displace at normal load, but was significantly overweight for unknown reasons and actually displaced . She had an overall length of , a beam of , and a draft of , deeper than designed. Her crew numbered 328 officers and enlisted men.
Yūbaris propulsion system was derived from that of the s, enlarged by one additional propeller shaft, steam turbine and four Kampon water-tube boilers. The three turbines used steam provided by eight boilers that operated at a pressure of and a temperature of . The turbines developed a total of and were intended to give the cruiser a speed of , but the increase in draft adversely affected both her speed and range. Yūbari only reached from , rather than her intended , when the ship ran her sea trials on 5 July 1923. The ship carried a maximum of of fuel oil that gave her a range of , reduced from her designed range of , at . Hiraga trunked the forward funnel aft into the rear funnel to minimize the effects of hot exhaust gases on the bridge personnel.
Armament and fire control
The cruiser's main battery consisted of six 50-caliber 3rd Year Type guns arranged in two twin-gun turrets and two single gun mounts protected by gun shields. One mount of each type was positioned forward and aft of the superstructure in a superfiring arrangement with the single mount positioned below the twin-gun turret. A pair of rotating Type 8 twin-tube mounts for torpedoes were located amidships on the ship's centerline. Each tube was provided with a single reload torpedo. A single 40-caliber 3rd Year Type anti-aircraft (AA) gun and two Lewis machine guns on a raised platform between the torpedo mounts for anti-aircraft defense. Yūbari was fitted with six rails at the stern that could accommodate 48 No. 1 naval mines in 24 compartments in the hull.
