was a light cruiser built for the Imperial Japanese Navy (IJN) during World War II, and was the only ship of her class completed before the end of the war. Designed to command submarine operations, she was obsolete upon completion in 1943. The ship was used as a transport and to escort the navy's capital ships for the rest of the year. Ōyodo was lightly damaged by American aircraft in early January 1944 during one transport mission and returned home several months later to begin conversion to serve as the flagship of the Combined Fleet.
The ship reverted to her previous roles when the headquarters of the Combined Fleet was moved ashore in September. The following month, she participated in the Battle off Cape Engaño, where she escorted the Japanese carriers attempting to decoy the American carrier fleet supporting the invasion of Leyte away from the landing beaches. Afterwards, the ship was transferred to Southeast Asia and engaged American forces in the Philippines in December where she was slightly damaged by American bombers. In early 1945, Ōyodo participated in Operation Kita, during which she transported aviation gasoline and other strategic materials back to Japan. The ship was damaged by American carrier aircraft in March and repairs were completed two months later. She was sunk with the loss of about 300 men during American airstrikes in July. After the war, Ōyodo was salvaged and scrapped in 1947–1948.
Background
The IJN's concept of submarine warfare was to use long-range submarines in squadrons (sentai) to attack enemy units at extended ranges. These submarines would be coordinated by a cruiser, which would use reconnaissance aircraft to provide targeting information. Originally, it was intended that the s would be able to serve in this role, but they proved unsatisfactory. By the late 1930s, the Japanese Navy had defined the need for seven cruisers to support its seven submarine squadrons. Funding for the first two vessels was approved under the 1939 4th Replenishment Program, of which only one, Ōyodo, was begun. Construction of the second ship, intended to be named Niyodo, was suspended on 6 November 1941 because Ōyodo still occupied her intended slipway and was finally cancelled on 3 August 1942.
Design and description
Ōyodos design was derived from that of the . Ōyodo retained the same general hull design with a flush deck and bulbous bow, but her superstructure and armament differed to suit her different role. Ōyodo had a length of overall, a beam of and a draft of . The ship displaced and had a metacentric height of at deep load. Her crew numbered 33 officers and 532 enlisted men as completed.
Ōyodo was powered by four geared steam turbine sets, each driving a single three-bladed propeller, using steam provided by six Kampon water-tube boilers that operated at a pressure of and a temperature of . The turbines were designed to produce for a speed of . The ship exceeded her designed speed during her sea trials reaching from . She stowed of fuel oil, which gave her a range of at . Ōyodo had three turbo generators of capacity and two diesel generators.
Armament and fire control
The ship's main battery comprised six 50-caliber 155 mm (6.1 in) 3rd Year Type guns in two triple-gun turrets superfiring forward of the superstructure. The gun was originally developed as a dual-purpose (anti-surface and anti-aircraft) weapon for the ; when they had their triple 155 mm turrets replaced with twin 203 mm (8 in) turrets, the now-surplus turrets were mounted on Ōyodo (as well as the s). Their slow rate of fire of 5 rounds per minute and limited elevation (up to only 55 degrees) made them unsuitable for the anti-aircraft role. The guns fired shells at a muzzle velocity of to a maximum range of at +45 degrees of elevation. Each gun was provided with 150 rounds.
Ōyodos heavy anti-aircraft battery consisted of eight 65-caliber 100 mm (3.9 in) Type 98 dual-purpose guns in four twin mounts. The anti-aircraft armament was completed by eighteen 60-caliber Type 96 light AA guns in six triple mounts.
The ship was equipped with a director-control tower above the bridge with a Type 94 gunnery director controlling the main armament. The director was fitted with a rangefinder and the upper gun turret mounted a rangefinder. The Type 98 10 cm guns were controlled by a pair of Type 94 directors positioned at the base of the bridge and the light AA guns were provided with three Type 95 directors, all on the forward superstructure.
Protection
The ship's armor was designed to protect against 155 mm shells and bombs dropped from an altitude of . It had a waterline belt had a maximum thickness of of copper alloy homogeneous armor that protected the propulsion machinery and the bomb magazine; it extended above the waterline and below. The armored deck rested on the upper edge of the belt armor and was thick except over the bomb magazine where it increased to . The ends of the belt armor were closed off by transverse bulkheads that also increased to 50 mm adjacent to the bomb magazine. The magazine itself had 35 mm sides and a 25 mm front. The steering gear aft was protected by an armored box with sides, a front and a 25 mm rear.
Forward of the boiler rooms, the fire-control center, the 25 mm and 155 mm magazines had armored sides. The latter magazine had plates that tapered to 40 mm at their lower edge. The armor on the other compartments was 60 mm thick reducing to 30 mm at the bottom. The roof of these spaces was 50 mm thick over the 155 mm magazines and reduced to 28 mm over the other compartments. The main gun turrets were protected by 25 mm homogeneous armor plates and their barbettes had 20 mm or 25 mm thick plates. The sides of the conning tower were 40 mm thick and it had a roof 20 mm thick.
Construction and career
Following the Japanese ship-naming conventions for light cruisers, the ship was named after the Ōyodo River in Kyūshū. Ōyodo was laid down at Kure Naval Arsenal on 14 February 1941, launched on 2 April 1942 and completed on 28 February 1943 On 1 April, she was assigned to the Third Fleet and was transferred to the Main Body, Mobile Force, a month later. In response to the invasion of Attu Island on 11 May, Ōyodo rendezvoused with three battleships, two aircraft carriers and five heavy cruisers in Tokyo Bay on 22 May. The Americans recaptured Attu before the fleet could depart to counterattack. The following month the ship received a brief refit in Kure.
Vice Admiral Jisaburō Ozawa, commander of the Third Fleet, hoisted his flag aboard the ship on 6 December. On 30 December Ōyodo participated in an operation to reinforce the garrisons at Rabaul and Kavieng. While returning to Truk on 1 January 1944, Ōyodo was slightly damaged by US aircraft from two aircraft carriers of Task Group 50.2, with two crewmen killed and six wounded. The following day, she rescued 71 survivors from the transport Kiyosumi Maru, which had been torpedoed by an American submarine. Ōyodo returned to Yokosuka on 16 February following the successful American invasion of Kwajalein, and loaded torpedoes and supplies for the Japanese garrison at Saipan, which were delivered on 22 February.
Ōyodo rejoined the Main Body of the 1st Mobile Fleet, commanded by Ozawa, on 5 October and departed Yokosuka on 11 October. En route, she was attacked by the submarine which fired six torpedoes, all of which missed. The ship departed Yashima anchorage on 20 October 1944 towards the Philippines as part of Operation "Sho-Ichi-Go"— which was intended to defeat the American invasion of the Philippines. Ōyodo was part of Ozawa's Northern Mobile ("Decoy") Force, which was to bait the American aircraft carrier strike force away from the main Japanese strike force by exposing the surviving Japanese carriers. Ōyodo was the only warship in Ozawa's force that had reconnaissance floatplanes, and both E13A1's performed reconnaissance and anti-submarine patrols over the fleet.
thumb|right|Ōyodo maneuvering through Allied gunfire, while begins sinking
thumb|right|Vice Admiral Ozawa transfers his flag to Ōyodo from the carrier
Although they had lost contact during the night, the Americans did find the Japanese carriers at 07:35. They had already launched an airstrike of 180 aircraft that was orbiting ahead of the American carriers while waiting for the Japanese ships to be located. This was just the first of a total of five airstrikes that the Americans launched that day. During the first strike, Ōyodo suffered two near-misses, but at 08:48 she was hit by a bomb that damaged a boiler room. At 10:54, Vice Admiral Ozawa left the sinking aircraft carrier and transferred his flag to Ōyodo. Later in the day the ship was hit by two rockets from F6F Hellcat fighter-bombers and damaged by another near-miss and Ozawa ordered his remaining forces to retire northward. Around 19:00 Ozawa learned about a force of destroyers and cruisers that sank the light carrier and drove off the Japanese destroyers rescuing survivors from some of the carriers lost earlier in the day. He ordered the two hybrid battleship/carriers and Ōyodo to reverse course and engage the Americans, but they were unable to find them, and they reversed course at 23:30 and headed for Amami Ōshima. When they arrived there on the 27th Ozawa transferred his flag to the battleship
thumb|Ōyodo being scrapped in Kure, 27 April 1948
On 24 July US Task Force 38 launched a massive attack to destroy any and all remaining units of the Japanese Navy. Ōyodo was strafed and hit by five bombs, two of which hit near her catapult and punched holes in her deck. Two more hit amidships near the engine rooms and the last struck forward of the bridge and started a fire that could not be extinguished for two days. Four days later, a day-long attack was launched by the US carrier fleet. Ōyodo was near-missed by bombs in the morning and the shock waves from their detonations ruptured her hull plating abreast of the forward engine room and No. 5 boiler room that flooded those two compartments. The asymmetric weight of the water on the starboard side caused her to capsize to starboard in shallow water about 25 minutes later. Permission to abandon ship was granted by Captain Shoichi Taguchi before she capsized, but about 300 crewmen were killed.