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.

In early 1945, Ōyodo participated in Operation Kita, during which she transported aviation gasoline and other strategic materials back to Japan.

She stowed 2,445 t (2,406 long tons) of fuel oil,[5] which gave her a range of 10,600 nautical miles (19,600 km; 12,200 mi) at 18 knots (33 km/h; 21 mph).

[7] 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.

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.

[10] The anti-aircraft armament was completed by eighteen 60-caliber 25 mm (1.0 in) Type 96 light AA guns in six triple mounts.

[11] The ship was equipped with a director-control tower above the bridge with a Type 94 gunnery director controlling the main armament.

The weight saved by not fitting torpedo tubes was invested instead in a hangar that could house four floatplanes, with two more stowed on deck, and a heavy-duty 44-meter (144 ft) catapult that was necessary for the new Kawanishi E15K Shiun floatplane (Allied reporting name "Norm") that was intended to perform reconnaissance for the submarine flotilla in areas where the enemy had air superiority.

[12] The ship's armor was designed to protect against 155 mm shells and 250-kilogram (550 lb) bombs dropped from an altitude of 3,000 meters (9,800 ft).

[14] Following the Japanese ship-naming conventions for light cruisers, the ship was named after the Ōyodo River in Kyūshū.

[15] The war had developed in ways unanticipated by the IJN and her designed role as a submarine flotilla flagship was no longer necessary or even possible, so the navy settled on using her as an ordinary light cruiser or as a transport.

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.

[15] Vice Admiral Jisaburō Ozawa, commander of the Third Fleet, hoisted his flag aboard the ship on 6 December.

The Americans finally spotted Ozawa's ships at 16:40, some 200 miles (320 km) east of Cape Engaño, the northeastern tip of Luzon.

They had already launched an airstrike of 180 aircraft that was orbiting 50 miles (80 km) ahead of the American carriers while waiting for the Japanese ships to be located.

At 10:54, Vice Admiral Ozawa left the sinking aircraft carrier Zuikaku 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.

On 24 December Ōyodo, the heavy cruiser Ashigara and six destroyers sortied to attack the American forces at San Jose on the island of Mindoro.

They were spotted by American aircraft late the next day and Ōyodo was hit by a pair of 500 lb (230 kg) bombs; one failed to detonate and the other only slightly damaged the cruiser.

The destroyers engaged an American convoy escorted by PT boats while the cruisers fired star shells to illuminate the area.

The ships were loaded with critically needed strategic war supplies (aviation gasoline, rubber, tin, zinc, and mercury) and 1,150 surplus oil workers to be ferried back to Japan.

The ships sailed from Singapore on 10 February and was spotted by the British submarine HMS Tantalus the following day.

Later that afternoon, Ōyodo launched one of her floatplanes which spotted the submarine USS Bashaw on the surface ahead of the convoy.

Hyūga opened fire with her main guns and forced Bashaw to submerge when one of her shells landed within 1,600 meters (1 mi) of the submarine.

Near-misses ruptured some hull plating forward and the cruiser started to flood, but she was towed to Etajima and beached to prevent her from sinking.

[20] On 24 July US Task Force 38 launched a massive attack to destroy any and all remaining units of the Japanese Navy.

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.