The impending American invasion of Luzon caused the IJN to order her to transport aircraft and supplies to the Philippines in December.

The ship was torpedoed and sunk by the American submarine USS Redfish in the East China Sea during the voyage.

The last purpose-built Japanese carrier construction was a group of vessels based on an improved Hiryū design, but with individual units differing in detail reflecting the changing circumstances as the conflict in the Pacific approached its conclusion.

A small island was mounted well forward on the starboard side and contained the ship's bridge and air operations control center.

The ship mounted a retractable crane on the starboard side of the flight deck, just aft of the rear elevator.

In 1943 the air group was revised to consist of 18 Mitsubishi A7M "Sam" fighters (+2 in storage), 27 Yokosuka D4Y "Judy" dive bombers and 6 Nakajima C6N "Myrt" reconnaissance aircraft.

When the ship was commissioned in 1944, neither the A7M nor the C6Ns were yet in service, so the air group was reconfigured to consist of 27 Zeros, 12 D4Ys, 3 of which were to be the reconnaissance version, and 9 Nakajima B6N "Jill" torpedo bombers.

By this time, however, the shortage of carrier-qualified aircrew was such that they were ordered to operate from shore bases and Unryū never embarked her full air group.

She underwent shakedown and trials within Tokyo Bay through mid-September, and was then transferred to Kure Naval District, from which she made numerous training runs around the Seto Inland Sea until December.

[13] On 13 December 1944, thirty Yokosuka MXY7 Ōhka kamikaze rocket planes were loaded aboard Unryū for transport to Manila in the Philippines.

Four days later, on 17 December 1944, Unryū departed Kure, Hiroshima escorted by the destroyers Shigure, Hinoki, and Momi under the overall command of Captain Konishi.

Her maiden sea voyage was a vain attempt to reinforce the garrison on the island of Luzon just prior to the Allied landings there.

The resulting explosion caused the warheads of the Ohka kamikaze planes stored on the lower hangar deck to detonate and essentially blew the bow off the ship.