Ukuru-class escort ship

The Ukuru-class escort ships (鵜来型海防艦, Ukuru-gata kaibōkan) were a class of twenty kaibōkan escort vessels built for the Imperial Japanese Navy during World War II.[1] The class was also referred to by internal Japanese documents as the "Modified B-class" coastal defense vessel (改乙型海防艦, Kai-Otsu-gata kaibōkan), and they were the fourth class of kaibōkan.

Uku in 1944
Class overview
NameUkuru class
Operators
Preceded byMikura class
Succeeded by
SubclassesHiburi class
Built1942–1944
In commission1943–1964
Planned142
Completed29
Cancelled2
Lost10
General characteristics
TypeEscort vessel
Displacement940 long tons (955 t) standard
Length77.7 m (255 ft)
Beam9.1 m (29 ft 10 in)
Draught3.05 m (10 ft)
Propulsion2 shaft, geared diesel engines, 4,400 hp (3,281 kW)
Speed19.5 knots (22.4 mph; 36.1 km/h)
Range5,000 nmi (9,300 km) at 16 kn (18 mph; 30 km/h)
Complement150
Sensors and
processing systems
  • Type 22 and 13 radars
  • Type 93 and/or Type 3 sonar
Armament
Shiga while she was preserved in Chiba City.

Background

The Mikura class escort ship was developed after the start of the Pacific War, it became apparent that a design more capable of anti-submarine warfare than the previous Shimushu and Etorofu class kaibōkan was needed. Despite being a simplified design, the Mikura-class vessels still took too long to construct, and due to the high attrition of Japan's destroyer and escort ships, action needed to be urgently taken to produce more ships in a quicker time. Furthermore, operational experience had shown that the Mikura-class was still very weak in its anti-aircraft capability.

The first five of the new Ukuru-class were authorized under the 1941 Rapid Naval Armaments Supplement Programme and an additional six in the 1942 Modified 5th Naval Armaments Supplement Programme and nine under the 1944 Wartime Naval Armaments Supplement Programme. Twenty vessels were commissioned; two more (Urumi and Murotsu) were launched by Uraga Dock and completed in August 1945 but were still uncommissioned by the war’s end. In addition to these, nine units and two additional unfinished ships belong to a sub-class called the Hiburi class[2] and are included in the table below.

Description

The Ukuru-class was a further simplification of the Mikura design. The hull was constructed using prefabricated sections which avoided the use of shaped steel or curved plates, which greatly reduced construction time. The curved plates on the bridge were also eliminated, and the smoke stacks were made of hexagonal elements instead of with a circular or oval cross-section. Internally, individual crew quarters were eliminated, becoming a communal area, and overall the construction was very spartan. These changes reduced construction time to under four months, although construction was often hindered by the lack of diesel engines.[2]

The main battery was the same as on the Mikura-class, with three dual-purpose Type 10 120 mm AA guns one forward, and a twin mount aft, but the later ships in the class were fitted with modified gun shields. Anti-aircraft protection was by five triple-mount Type 96 25-millimeter (1.0 in) anti-aircraft guns with two abreast the bridge, one of each side of the smokestack, and one aft on the deck house, along with a single-mount in front of the bridge. Some units received additional single-mount Type 96s, which were located on the forecastle. The Ukuru-class was equipped with the Type 22 and Type 13 radar. The Ukuru class was initially armed with 120 depth charges with two Type 94 depth charge projectors, sixteen Type 3 depth charge throwers and two depth charge chutes at the stern. The ships were provided with a Model 93 sonar and a Type 93 hydrophone; later units received the Type 3 Model 2 sonar, and some would later receive an 8 cm (3 in) trench mortar.[2]

Initially, the class retained capacity as a minesweeper, and was equipped with two paravanes; however, this was removed soon after completion.[2]

Operational service

Despite being easy to build, they proved quite durable, with 11 occurrences of the class striking mines and only 3 sinking, one of which was after the war. Ikuna survived being torpedoed by USS Crevalle and striking a mine as well.

The Ukuru vessels were used extensively on convoy escort assignment in the South China Sea and East China Sea, where they frequently were attacked by Allied submarines or aircraft. However, despite their durability, they proved to be relatively ineffective against Allied submarines. Okinawa was the most successful ship of the class, helping to sink two US submarines, USS Snook on April 14, 1945 with the kaibōkan CD-8, CD-32, and CD-52; and USS Bonefish on June 19, 1945 with kaibokan CD-63, CD-75, CD-158, and CD-207.

Surviving ships were used in the immediate postwar period as minesweepers and for repatriation. Five vessels survived to return to Japanese control, and were used as weather survey ships or as patrol ships, with the last being retired in 1966.[2]

Ships
Number Kanji Name Builder Laid down Launched Completed Fate
#328 日振 Hiburi Hitachi, Sakurajima 3 January 1944 10 April 1944 27 June 1944 Torpedoed and sunk by USS Harder on 22 August 1944, with 154 killed and wounded.
#332 鵜来 Ukuru Nihon Kokan, Tsurumi 9 October 1943 15 May 1944 31 July 1944 Ukuru survived the war and later became a weather survey ship in the Japanese Maritime Transport Bureau before being sold for scrapping on 24 November 1965.[3]
#333 大東 Daitō Hitachi, Sakurajima 23 February 1944 24 June 1944 7 August 1944 Daitō survived the war, but was lost while minesweeping shortly after the war ended on 16 November 1945.
#335 沖縄 Okinawa Nihon Kokan, Tsurumi 10 December 1943 19 June 1944 16 August 1944 Okinawa was damaged by a bomb in an air attack by P-38s while escorting TA no. 2 on 5 November 1944 and damaged by PT boats on 9 November and by aircraft again on 18 November 1944. Okinawa was sunk on 30 July 1945 by aircraft from HMS Formidable.
#336 奄美 Amami Nihon Kokan, Tsurumi 14 February 1944 30 November 1944 8 April 1945 Amami survived the war and was ceded to the UK as a war reparation and scrapped on 20 December 1947.
#337 粟国 Aguni Nihon Kokan, Tsurumi 15 February 1944 21 September 1944 2 December 1944 On 27 May 1945, Aguni was damaged by a Bat glide bomb. The bomb's 1,000 lb (450 kg) warhead exploded off Aguni's starboard bow demolishing the whole foredeck area ahead of the bridge and killing 33 sailors. After being hit, Aguni's crew had to cut her anchor chain to free her. Kaibokan CD-12 was dispatched to assist Okinawa in rescuing Aguni’s crew, but despite the heavy damage the kaibokan remained navigable and proceeded stern first to Pusan, Korea on her own power. Aguni survived the war and was sold for scrapping on 20 May 1948.
#338 新南 Shinnan Uraga Dock Company 30 June 1944 4 September 1944 21 October 1944 Shinnan survived the war and later became a weather survey ship in the Japanese Maritime Transport Bureau before being sent to the petrol development agency in October 1967. She was scrapped in 1975.
#339 昭南 Shōnan Hitachi, Sakurajima 23 February 1944 19 May 1944 13 July 1944 Torpedoed and sunk by USS Hoe on 25 February 1945, with 198 crew and passengers killed.
#4701 稲木 Inagi Mitsui Zosensho, Tamano 15 May 1944 25 September 1944 16 December 1944 Inagi was bombed and sunk by planes from HMS Formidable on 9 August 1945, with the loss of 29 killed and 35 wounded.
#4702 羽節 Habushi Mitsui Zosensho, Tamano 20 August 1944 20 November 1944 10 January 1945 Habushi struck a mine on 8 April 1945 and was damaged. She survived the war and was ceded to the United States as a war reparation and scrapped starting 17 October 1947.
#4703 男鹿 Ojika Mitsui Zosensho, Tamano 7 September 1944 30 December 1944 21 February 1945 Ojika was torpedoed and sunk by USS Springer on 2 June 1945.
#4704 金輪 Kanawa Mitsui Zosensho, Tamano 15 November 1944 20 January 1945 25 March 1945 Kanawa survived the war and was ceded to the UK as a war reparation and scrapped on 14 August 1947.
#4705 宇久 Uku Sasebo Navy Yard 1 August 1944 12 November 1944 30 December 1944 Uku struck a mine on 9 April 1945 and was damaged. She survived the war and was ceded to the United States as a war reparation and later scrapped.
#4707 高根 Takane Mitsui Zosensho, Tamano 15 December 1944 13 February 1945 26 April 1945 Takane survived the war and was scrapped starting 27 November 1947.
#4709 久賀 Kuga Sasebo Navy Yard 1 August 1944 19 November 1944 25 January 1945 Kuga struck a mine on 25 June 1945 and was damaged. She survived the war and was scrapped on 30 June 1947.
#4711 志賀 Shiga Sasebo Navy Yard 25 November 1944 9 February 1945 20 March 1945 Shiga survived the war and later became a weather survey ship in the Japanese Maritime Transport Bureau before being discarded on May 6, 1964. Her hull became the pavilion for Maritime Amusement Park in Chiba City, but her hull deteriorated because of poor maintenance and was dismantled and scrapped in 1998.[4]
#4712 伊王 Iwō Maizuru Navy Yard 25 November 1944 12 February 1945 24 March 1945 Iwo struck a mine on 13 June 1945 and was damaged. She was damaged lightly in an air attack by planes from USS Shangri-La, losing 4 killed and 61 wounded. She survived the war and was scrapped starting 2 July 1948.
#5251 屋久 Yaku Uraga Dock Company 30 June 1944 4 September 1944 23 October 1944 Torpedoed and sunk by USS Hammerhead on 23 February 1945, with the loss of 132 men.
#5252 久米 Kume Hitachi, Sakurajima 26 May 1944 15 August 1944 25 September 1944 Torpedoed and sunk by USS Spadefish on 28 January 1945, with the loss of 89 men.
#5253 竹生 Chikubu Uraga Dock Company 8 September 1944 12 November 1944 31 December 1944 Chikubu survived the war and later became a weather survey ship in the Japanese Maritime Transport Bureau before being sold for scrapping on 4 October 1962.
#5254 生名 Ikuna Hitachi, Sakurajima 30 June 1944 4 September 1944 15 October 1944 Ikuna was hit by a torpedo by USS Crevalle and damaged on 10 April 1945. On 1 August she struck a mine and was damaged. Ikuna survived the war and later became a weather survey ship in the Japanese Maritime Transport Bureau before being sold for scrapping on 25 May 1963.
#5255 神津 Kōzu Uraga Dock Company 20 October 1944 31 December 1944 7 February 1945 She survived the war and was ceded to the Soviet Union as a war reparation on 28 August 1947. Served in Soviet Pacific Ocean Fleet as patrol ship EK-47 (1947), oceanographic research ship Nord (1948), later - Glubomer (1953), repair ship PM-62 (1955). Decommissioned on 25 January 1969 and scrapped.
#5256 保高 Hodaka Uraga Dock Company 27 November 1944 28 January 1945 30 March 1945 She survived the war and was ceded to the United States as a war reparation and scrapped starting 1 March 1948.
#5257 四阪 Shisaka Hitachi, Sakurajima 21 August 1944 31 October 1944 15 December 1944 She survived the war and was ceded to the Republic of China Navy as a war reparation and renamed as Huai An (惠安), but later was captured by the Chinese communists at the end of Chinese Civil War, and entered PLAN under the same name. The ship was later renamed as Rui Jin (瑞金) and served as a training ship in PLAN until the early 1980s before it as finally scrapped.
#5258 伊唐 Ikara Uraga Dock Company 26 December 1944 22 February 1945 30 April 1945 On 9 August 1945, Ikara struck a mine and sank.
#5259 崎戸 Sakito Hitachi, Sakurajima 7 September 1944 29 November 1944 10 January 1945 On 27 June 1945, Sakito struck a mine and was damaged. Sakito survived the war and was scrapped on 1 December 1947.
#5260 生野 Ikuno Uraga Dock Company 3 January 1945 11 March 1945 17 July 1945 She survived the war and was ceded to the Soviet Union as a war reparation on 29 July 1947. Served in Soviet Pacific Ocean Fleet as patrol ship EK-41 (1947), target ship TsL-41 (1948), oceanographic research ship Val (1949). Decommissioned on 1 June 1961 and scrapped.
#5263 目斗 Mokuto Hitachi, Sakurajima 5 November 1944 7 January 1945 19 February 1945 On 4 April 1945, Mokuto struck a mine and sank.
#5264 波太 Habuto Hitachi, Sakurajima 3 December 1944 28 February 1945 7 April 1945 Habuto struck a mine on 6 June 1945 and was damaged. She struck a second mine on 10 June 1945 and was again damaged. She survived the war and was ceded to the UK as a war reparation and scrapped on 16 July 1947.

Twelve other ships were cancelled in 1945 - numbers #4706, #4708, #4710, #4713 to #4721. These included Murotsu and Urumi (both launched but incomplete); also cancelled (unstarted) were #5261, #5262, #5267 to #5284 (all of the Yaku group) from the Modified 5th Naval Armaments Supplement Programme. Also cancelled incomplete were two of the Hiburi class - numbers #5265 (Ōtsu) and #5266 (Tomoshiri).

See also

Notes
  1. Worth p. 208
  2. Stille, Mark (2017). Imperial Japanese Navy Antisubmarine Escorts 1941–45. Oxford, UK: Osprey Publishing. pp. 30–33. ISBN 978-1-4728-1817-1.
  3. Her hull number PL104 is seen in a scene in the 1961 classic Japanese movie "Mothra".
  4. "Japanese Escorts".

References
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