Japanese aircraft carrier Chūyō

Nitta Maru in passenger service, 1940

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). She was laid down on 9 May 1938 as yard number 750, launched on 20 May 1939 and completed on 23 March 1940.[1][2] The IJN subsidized all three Nitta Maru-class ships for possible conversion into auxiliary aircraft carriers.[3] The ships were intended to upgrade NYK's passenger service to Europe and it was reported that Nitta Maru was the first ship to be fully air conditioned in the passenger quarters.[4] The ships had accommodation for 285 passengers (127 first class, 88 second and 70 third).[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.[5][6]

The 17,163-gross register ton (GRT) vessel had a length of 170.0 meters (557.8 ft), a beam of 22.5 meters (73.8 ft) and a depth of hold of 12.4 meters (40.7 ft). She had a net tonnage of 9,397 and a cargo capacity of 11,800 tons.[4][7] The ship was powered by two sets of geared steam turbines made by the shipbuilder, each driving one propeller shaft, using steam produced by four water-tube boilers.[7] The turbines were rated at a total of 25,200 shaft horsepower (18,800 kW)[8] that gave her an average speed of 19 knots (35 km/h; 22 mph)[2] and a maximum speed of 22.2 knots (41.1 km/h; 25.5 mph).[8][Note 1]

The ship was requisitioned for use as a military transport in February 1941. She made a few voyages, including one transferring roughly 1,200 American prisoners of war from Wake Island to Japan in January 1942. The ship departed on 12 January, arriving in Yokohama six days later. After unloading 20 men there, she departed for China. En route, the Japanese commander of the guard contingent, Lieutenant Toshio Sato, picked five men at random and ordered them topside. There they were ordered to kneel and he told them in Japanese: "You have killed many Japanese soldiers in battle. For what you have done you are now going to be killed ... as representatives of American soldiers." The Japanese then beheaded them. The bodies were used for bayonet practice and then thrown overboard.[10]

Later that year the IJN decided to convert her to an escort carrier, matching her sisters Taiyō and Un'yō. 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.[12] The Taiyō-class carriers had a flush-decked configuration that displaced 18,116 metric tons (17,830 long tons) at standard load[13] and 20,321 metric tons (20,000 long tons) at normal load. The ships had an overall length of 180.2 meters (591 ft 4 in), a beam of 22.5 meters (73 ft 10 in) and a draft of 7.7 meters (25 ft 5 in).[9] The flight deck was 172.0 meters (564 ft 3 in) long and 23.5 meters (77 ft) wide and no arresting gear was fitted. They had a single hangar, approximately 91.4 meters (300 ft) long, served by two centreline aircraft lifts, each 12.0 by 13.0 meters (39.4 ft × 42.7 ft). Chūyō could accommodate a total of 30 aircraft, including spares.[14]

The changes made during the conversion limited the ship to a speed of 21.4 knots (39.6 km/h; 24.6 mph). She carried 2,290 metric tons (2,250 long tons) of fuel oil that gave her a range of 8,500 nautical miles (15,700 km; 9,800 mi) at a speed of 18 knots (33 km/h; 21 mph).[1][Note 2] Chūyō's crew numbered 850 officers and ratings.[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. Her light AA consisted of eight license-built 25 mm (1.0 in) Type 96 light anti-aircraft (AA) guns in four twin-gun mounts, also in sponsons along the sides of the hull. In early 1943, the four twin 25 mm mounts were replaced by triple mounts and additional 25 mm guns were added. Chūyō had a total of 22 guns plus 5 license-built 13.2 mm (0.5 in) Type 93 anti-aircraft machineguns.[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.[1][18] They were thus relegated to secondary roles; Chūyō was used primarily as an aircraft transport to and from the naval base at Truk. She made the first of her 13 trips on 12 December 1942 and was back in Yokosuka two weeks later. She made about one trip per month in 1943 and the first eventful voyage was in April. 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. On 9 April, the carrier was attacked by the submarine USS Tunny, but the detonators for the Mark 14 torpedoes were defective, causing them either to detonate early or not to detonate at all, denting Chūyō's hull.[11]

The ship made four more trips between April and August, accompanied by her sister ship Un'yō each time, before she was given a brief refit between 9 and 18 August. The next voyage began on 7 September, this time with Taiyō in company. During the return leg on 24 September, the latter was torpedoed by USS Cabrilla. With one of Taiyō's propeller shafts damaged, Chūyō had to tow her for two days before they reached Yokosuka. 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.[11]

On 30 November, the carrier departed Truk in company with the light carrier Zuihō and her sister Un'yō; the carriers were escorted by the heavy cruiser Maya and four destroyers. Chūyō and Un'yō had aboard 21 and 20 captured crewmen from the sunken submarine USS Sculpin, respectively. At 10 minutes after midnight on 4 December, Chūyō was hit in the bow by a torpedo fired by USS Sailfish at 32°30′N 143°40′E. The detonation blew off her bow and caused the forward part of the flight deck to collapse. To reduce pressure on the interior bulkheads, the ship's captain began steaming in reverse at half speed towards Yokosuka. Nearly six hours later, she was again torpedoed by Sailfish at 05:55, this time twice in the port engine room, at 31°55′N 143°30′E. The hits disabled her engines and Maya and one destroyer came alongside to render assistance. Sailfish attacked again at 08:42 and hit the carrier with one or two torpedoes on the port side. The hits caused massive flooding and Chūyō capsized very quickly to port six minutes later. There were very few survivors because of the speed at which she sank.[11] Only 161 crewmen and passengers were saved, including one American prisoner of war;[19] 737 passengers and 513 crewmen were lost.[Note 3] She was stricken from the Navy Directory on 5 February 1944.[11]

• Itaru Tachibana (spy) - Boarded on 21 June 1941 from San Francisco to Japan, forced to leave the U.S. due to being accused of espionage.[20]

• List by death toll of ships sunk by submarines

• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. Greenwich: Conway Maritime Press. ISBN 0-85177-146-7.
• Jentschura, Hansgeorg; Jung, Dieter & Mickel, Peter (1977). Warships of the Imperial Japanese Navy, 1869–1945. Annapolis, Maryland: United States Naval Institute. ISBN 0-87021-893-X.
• Peattie, Mark (2001). Sunburst: The Rise of Japanese Naval Air Power 1909–1941. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-432-6.
• Polmar, Norman & Genda, Minoru (2006). Aircraft Carriers: A History of Carrier Aviation and Its Influence on World Events. Vol. 1, 1909–1945. Washington, D.C.: Potomac Books. ISBN 1-57488-663-0.
• Stille, Mark (2005). Imperial Japanese Navy Aircraft Carriers 1921–1945. New Vanguard. Vol. 109. Oxford, UK: Osprey Publishing. ISBN 1-84176-853-7.
• Tate, E. Mowbray (1986). Transpacific Steam: The Story of Steam Navigation from the Pacific Coast of North America to the Far East and the Antipodes, 1867–1941. New York: Cornwall Books. ISBN 0-8453-4792-6.OCLC 12370774
• Tully, Anthony P. (2007). "IJN Chuyo: Tabular Record of Movement". Imperial Japanese Navy Page. Combined Fleet.com. Retrieved 5 November 2015.
• Watts, Anthony J. & Gordon, Brian G. (1971). The Imperial Japanese Navy. Garden City, New York: Doubleday. ISBN 0385012683.

• Imperial Japanese Navy Page