She spent most of her service ferrying aircraft, cargo and passengers to Truk until she was torpedoed and sunk by an American submarine in late 1943 with heavy loss of life.

Nitta Maru was the lead ship of her class and was built by Mitsubishi Shipbuilding & Engineering Co. at their Nagasaki shipyard for Nippon Yusen Kaisha (NYK).

[4] The start of World War II in September 1939 restricted them to the Pacific and they served on the San Francisco run until the Japanese Government declared a ban on all voyages to the United States in August 1941.

She made a few voyages, including one transferring roughly 1,200 American prisoners of war from Wake Island to Japan in January 1942.

En route, the Japanese commander of the guard contingent, Lieutenant Toshio Sato, picked five men at random and ordered them topside.

The conversion took place in Kure Naval Arsenal between 1 July and 25 November 1942[11] and the ship was renamed Chūyō on 31 August.

[15] The ship was equipped with eight 40-caliber 12.7 cm (5.0 in) Type 89 dual-purpose guns in four twin mounts on sponsons along the sides of the hull.

[16] The ships also received a Type 13 air search radar in a retractable installation on the flight deck at that time.

[17] The slow speed and lack of arresting gear prevented the Taiyōs from supporting the main fleet as the IJN had intended.

Together with her sister Taiyō and the heavy cruiser Chōkai, and escorted by six destroyers, Chūyō departed Yokosuka on 4 April and made a brief stopover at the island of Saipan three days later.

Although she was transferred to the Combined Fleet on 27 September and then to the Grand Escort Command on 15 November, it made no appreciable difference to her duties as the ship continued to ferry aircraft to Truk.

To reduce pressure on the interior bulkheads, the ship's captain began steaming in reverse at half speed towards Yokosuka.