Japanese aircraft carrier Un'yō

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IJN CV Unyo in 1943 cropped.jpg
Un'yō in military service in 1943
Empire of Japan
Name: Yawata Maru
Operator: NYK Line house flag.svg Nippon Yusen Kaisha
Builder: Mitsubishi Shipbuilding & Engineering Co., Nagasaki, Japan
Yard number: 751
Laid down: 14 December 1938
Launched: 31 October 1939
Completed: 31 July 1940
In service: 1940
Fate: Transferred to the Imperial Japanese Navy, 1941
Empire of Japan
Commissioned: 31 May 1942
Out of service: 17 September 1944
Renamed: Un'yō, 31 August 1942
Fate: Sunk by the submarine USS Barb, 17 September 1944
General characteristics (as converted)
Class and type: Taiyō-class escort carrier
  • 18,116 t (17,830 long tons) (standard)
  • 20,321 t (20,000 long tons) (normal)
Length: 180.2 m (591 ft 4 in) (o/a)
Beam: 22.5 m (73 ft 10 in)
Draft: 7.7 m (25 ft 5 in)
Installed power:
Speed: 21 knots (39 km/h; 24 mph)
Range: 6,500 or 8,500 nmi (12,000 or 15,700 km; 7,500 or 9,800 mi) at 18 knots (33 km/h; 21 mph)
Complement: 850
Aircraft carried: 30

Un'yō (雲鷹, Cloud Hawk) was a Taiyō-class escort carrier originally built as Yawata Maru (八幡丸), one of three Nitta Maru-class cargo liner built in Japan during the late 1930s. She was transferred to the Imperial Japanese Navy (IJN) during the Pacific War and was converted into an escort carrier in 1942. She spent most of her service ferrying aircraft, cargo and passengers to various bases in the Pacific until she was sunk by an American submarine in 1944.

Civilian service[edit]

Yawata Maru in passenger service

Yawata Maru was the second of three ships of the Nitta Maru-class and was built by Mitsubishi Shipbuilding & Engineering Co. at their Nagasaki shipyard for Nippon Yusen Kaisha (NYK). She was laid down on 14 December 1938 as yard number 751, launched on 31 October 1939 and completed on 31 July 1940.[1][2] The IJN subsidized all three Nitta Maru-class ships for possible conversion into auxiliary aircraft carriers.[3] The ships were intended for service to Europe, but the start of World War II in September 1939 restricted them to the Pacific.[4]

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 9,379.[5] The ship was powered by two sets of geared steam turbines, each driving one propeller shaft, using steam produced by four water-tube boilers. The turbines were rated at a total of 25,200 shaft horsepower (18,800 kW)[6] 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).[6][Note 1]

Military service[edit]

The ship was requisitioned by the Imperial Japanese Navy in October 1941. Initially, the ship was assigned for transporting prisoners of war. Between 25 November 1941 and 31 May 1942, Yawata Maru was converted into an escort carrier at Kure Naval Arsenal and the ship was renamed Un'yō on 31 August.[8] The Taiyō-class carriers had a flush-decked configuration that displaced 18,116 metric tons (17,830 long tons) at standard load[9] 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).[7] The flight deck was 172.0 meters (564 ft 3 in) long and 23.5 meters (77 ft) wide. 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).[10] Un'yō could accommodate a total of 30 aircraft, including spares,[3] although no arresting gear was fitted.[10]

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.[11]

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 four additional 25 mm triple mounts were added. She also received a Type 13 air search radar in a retractable installation on the flight deck at that time. The following year, Un'yō's light AA armament was increased to a total of 64 weapons.[12]

Un'yō made three voyages between July and October to bases in Truk, Saipan, and Rabaul, during which she delivered 10 Mitsubishi A6M Zero fighters to the latter on 11 September. Her next trip was far more involved as she ferried aircraft between Truk, the Philippines, Palau and the Dutch East Indies. The ship departed Yokosuka on 28 October and picked up the 2nd Fighter Regiment at Surabaya, Java on 2 December and delivered them to Truk on 11 days later. Un'yō returned to Surabaya on 24 December and loaded 33 aircraft of the Imperial Japanese Army's 1st Fighter Regiment for delivery to Truk before finally returning to Yokosuka in early January 1943.[13]

On 10 July 1943, off Truk, she was hit by a single torpedo fired by the submarine USS Halibut.

On 19 January 1944, while en route to Yokosuka, she was hit and heavily damaged by three torpedoes fired by USS Haddock. While sheltering at Garapan Anchorage, Saipan on 23 January, a follow-up attack by Halibut was driven off. Following repairs, she was back in service by June 1944.

On 17 September, Un'yō was struck by three torpedoes fired by USS Barb. Her crew’s struggle to keep Un'yō afloat was in vain. Of the approximately 1,000 people aboard (crew and passengers), 761 were rescued. The vessel's last position was 220 nautical miles (410 km; 250 mi) southeast of Hong Kong, 19°08′N 116°36′E / 19.133°N 116.600°E / 19.133; 116.600Coordinates: 19°08′N 116°36′E / 19.133°N 116.600°E / 19.133; 116.600.


  1. ^ Watts and Gordon and Stille say that the ship was originally equipped with diesel engines that were replaced during the conversion by steam turbines, but this is contradicted by Lloyd's Register.[5] This also seems unlikely as the conversion only took about five months when the conversion of the diesel-powered liner Argentina Maru (Kaiyō) took eleven months. In addition, the turbines in the latter were twice as powerful as those in the Taiyō-class ships[7] and would probably have been used if the IJN wanted to increase the speed of the Taiyōs.[1][3]
  2. ^ Other sources give a range of 6,500 nmi (12,000 km; 7,500 mi) at that speed.[7][10]


  1. ^ a b c Watts & Gordon, pp. 187–88
  2. ^ a b "Yawata Maru (4047477)"Paid subscription required. Miramar Ship Index. Retrieved 11 April 2017. 
  3. ^ a b c Stille, p. 40
  4. ^ Tate, pp. 68–69
  5. ^ a b "Lloyd's Register 1941–42" (PDF). PlimsollShipData. Lloyd's of London. Retrieved 6 November 2015. 
  6. ^ a b Jentschura, Jung & Mickel, p. 59
  7. ^ a b c Jentschura, Jung & Mickel, p. 58
  8. ^ Polmar & Genda, p. 262
  9. ^ Stille, pp. 40–41
  10. ^ a b c Peattie, p. 245
  11. ^ Chesneau, p. 185
  12. ^ Stille, p. 41
  13. ^ Tully


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