Background

• In 1937, the IJN planned this class as a replacement for the timeworn Natsushima
  Sokuten class auxiliary minelayer (1913)
  The was a class of minelayers of the Imperial Japanese Navy , serving during the 1910s and the World War II. They were called the Sokuten class from their nameship. And, they were called Toshima class after the Sokuten retired. Also, by the book, the Natsushima was included to this class...
  
   and the Sokuten-class auxiliary minelayer
  Sokuten class auxiliary minelayer (1913)
  The was a class of minelayers of the Imperial Japanese Navy , serving during the 1910s and the World War II. They were called the Sokuten class from their nameship. And, they were called Toshima class after the Sokuten retired. Also, by the book, the Natsushima was included to this class...
  
  .

Sokuten class

• Project number H11. Original model of the Sokuten class. Five vessels were built in 1937–40 under the Maru 3 Programme
  3rd Naval Armaments Supplement Programme (Japan, 1937)
  The otherwise known as the "Circle Three" Plan was the third of four expansion plans of the Imperial Japanese Navy between 1930 and the start of World War II.-Background:...
  
   (Ship # 57–61).

  Ship #	Ship	Builder	Laid down	Launched	Completed	Fate
  57		Mitsubishi, Yokohama Shipyard	24-06-1937	27-04-1938	28-12-1938	Sunk by aircraft at Palau Palau Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a... , 25-07-1944.
  58		Tōkyō Ishikawajima Shipyard	03-09-1937	25-06-1938	25-04-1939	Clashed with Army troop transport and sunk off Urup Urup Urup is an uninhabited volcanic island near in the south of the Kuril Islands chain in the Sea of Okhotsk in the northwest Pacific Ocean. Its name is derived from the Ainu language word for salmon trout.-Geography and climate:... , 03-03-1944.
  59		Mitsubishi, Yokohama Shipyard	24-03-1939	28-08-1939	20-06-1940	Sunk by USS Sennet USS Sennet (SS-408) USS Sennet , a Balao-class submarine, was a ship of the United States Navy named for the sennet, a barracuda.Sennet was laid down on 8 March 1944 by the Portsmouth Navy Yard in Kittery, Maine; launched on 6 June 1944, sponsored by Mrs. Roscoe W. Downs; and commissioned on 22 August 1944, Commander...  off Kii Peninsula Kii Peninsula The is the largest peninsula on the island of Honshū in Japan. The area south of the “Central Tectonic Line” is called Nankii , and includes the most poleward living coral reefs in the world due to the presence of the warm Kuroshio Current, though these are threatened by global warming and human...  32°10′N 135°58′E, 16-02-1945.
  60		Tōkyō Ishikawajima Shipyard	22-06-1938	29-06-1939	27-12-1939	Decommissioned on 05-09-1945. Surrendered to United Kingdom United Kingdom The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...  on 20-11-1947. Scrapped on 31-03-1948.
  61		Tōkyō Ishikawajima Shipyard	28-07-1939	09-12-1939	31-10-1940	Sunk by unknown submarine off Hatsushima, 16-11-1943.

Hirashima class

• Project number H11B. Second production model of the Sokuten-class. Nine vessels were built in 1939–43 under the Maru 4 Programme
  4th Naval Armaments Supplement Programme (Japan, 1939)
  The was one of the armaments expansion plan of the Imperial Japanese Navy .-Background:In 1939, the IJN started new naval armaments expansion plan...
  
   (Ship # 170–178). They were equipped with a 76.2 mm anti-aircraft gun. The Nuwajima had its ballast tank replaced with a fuel tank for convoy escort operations. These nine vessels were classed in the Sokuten-class in the IJN official documents.

  Ship #	Ship	Builder	Laid down	Launched	Completed	Fate
  170		Mitsubishi, Yokohama Shipyard	06-09-1939	06-06-1940	24-12-1940	Sunk by USS Sawfish USS Sawfish (SS-276) USS Sawfish , a Gato-class submarine, was a ship of the United States Navy named for the sawfish, a viviparous ray which has a long flat snout with a row of toothlike structures along each edge...  at west of Gotō Islands Goto Islands The are Japanese islands in the East China Sea, off the western coast of Kyūshū. The islands are a part of Nagasaki Prefecture.- Geography :There are 140 islands in total, including five main islands:,,,, and.... , 27-07-1943.
  171		Tama Shipyards	07-11-1940	08-09-1941	20-12-1941	Sunk by aircraft off Buka Island Buka Island Buka Island is the second largest island in the Papua New Guinean province of Bougainville.- History :Buka was first occupied by humans in paleolithic times, some 30,000 years ago... , 28-09-1943.
  172		Mitsubishi, Yokohama Shipyard	10-03-1941	13-08-1941	28-02-1942	Decommissioned on 30-11-1945. Surrendered to United States United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...  on 01-10-1947. Sunk as target at 35°40′N 122°53′E on 16-10-1947.
  173		Nihon Kōkan, Tsurumi Shipyard	11-12-1940	18-10-1941	25-03-1942	Sunk by aircraft at Okinawa Island Okinawa Island Okinawa Island is the largest of the Okinawa Islands and the Ryukyu Islands of Japan, and is home to Naha, the capital of Okinawa Prefecture. The island has an area of... , 10-10-1944.
  174		Ōsaka Iron Works, Sakurajima Factory	15-01-1941	15-11-1941	25-04-1942	Decommissioned on 22-10-1945. Surrendered to Republic of China Republic of China The Republic of China , commonly known as Taiwan , is a unitary sovereign state located in East Asia. Originally based in mainland China, the Republic of China currently governs the island of Taiwan , which forms over 99% of its current territory, as well as Penghu, Kinmen, Matsu and other minor...  on 03-10-1947, and renamed Yungtsin (PF-75). Decommissioned on 01-05-1960.
  175		Mitsui, Tamano Shipyard	12-07-1941	02-03-1942	31-08-1942	Struck a naval mine at Muroran Muroran, Hokkaido is a city and port located in Iburi, Hokkaidō, Japan. It is the capital city of Iburi Subprefecture.As of 2008, the city has an estimated population of 96,724 and a density of 1,210 people per km². The total area is 80.65 km².- History :...  on 04-10-1945. Decommissioned on 05-10-1945. Scrapped 1947.
  176		Nihon Kōkan, Tsurumi Shipyard	31-10-1941	04-07-1942	25-11-1942	Sunk by USS Cobia USS Cobia (SS-245) USS Cobia is a , formerly of the United States Navy, named for the cobia, a food fish found in warm waters.Cobia was laid down on 17 March 1943 by Electric Boat Co., Groton, Conn. She was launched on 28 November 1943 , and commissioned on 29 March 1944, Lieutenant Commander Albert L...  off Kota Bharu Kota Bharu Kota Bharu is a city in Malaysia, is the state capital and Royal City of Kelantan. It is also the name of the territory in which Kota Bharu City is situated. The name means 'new city' or 'new castle/fort' in Malay. Kota Bharu is situated in the northeastern part of Peninsular Malaysia, and lies... , 14-01-1945.
  177		Ōsaka Iron Works, Sakurajima Factory	26-11-1941	31-07-1942	15-11-1942	Heavy damaged by aircraft at Saiki Saiki, Oita is a city located in Ōita Prefecture, Japan.As of 2003, the former city had an estimated population of 49,183 and the density of 249.19 persons per km²... , 30-04-1945. Later sank in shallow water. Salvaged and scrapped on 01-09-1948.
  178		Nihon Kōkan, Tsurumi Shipyard	20-07-1942	18-04-1943	31-07-1943	Sunk by aircraft at Laoag City Laoag City The City of Laoag is a 1st class city in the province of Ilocos Norte, Philippines. It is the capital city of Ilocos Norte, and the province's political, commercial, and industrial hub. It is the location of the Ilocos region's only commercial airport... , 21-10-1944.
  179		Hitachi Zōsen				Cancelled on 11 August 1943.

Ajiro class

• Project number H13 at first. The IJN hoped urgent building for her. The Navy Technical Department
  Imperial Japanese Navy Technical Department
  The was the externally operating division of the Ministry of the Navy of Japan responsible for the administration of naval vessel construction. From 1923 onward, it took on the role of a research institution for the research and development of naval technologies and engineering...
  
   revised the Hirashima drawings. Twenty-six vessels were planned under the Maru Kyū Programme (Ship # 460–473, 14 vessels) and the Kai-Maru 5 Programme
  Modified 5th Naval Armaments Supplement Programme (Japan, 1942)
  The was one of the wartime armaments expansion plans of the Imperial Japanese Navy .-Background:In September 1942, after being defeated in the Battle of Midway, the IJN drew up a new armaments expansion plan. This plan was combined by the 5th Naval Armaments Supplement Programme and the 6th Naval...
  
   (Ship # 5421–5432, 12 vessels), but only Ajiro was completed. The Ajiro-class were classified separately from the Sokuten-class in the IJN official documents.

  Ship #	Ship	Builder	Laid down	Launched	Completed	Fate
  460		Hitachi Zōsen, Innoshima Shipyard	06-09-1943	08-04-1944	31-07-1944	Sunk by USS Snapper USS Snapper (SS-185) USS Snapper , a Salmon-class submarine, was the third ship of the United States Navy of the name and the second to be named for the snapper, any of numerous carnivorous, bass-like fishes, esteemed as food and as game fishes. Her keel was laid down by the Portsmouth Navy Yard on 23 July 1936. She...  at northwest of Chichi-jima Chichi-jima , formerly known as Peel Island and in the 19th century known to the English as part of the Bonin Islands, is the largest island in the Ogasawara archipelago. Chichi-jima is approximately 150 miles north of Iwo Jima. The island is within the political boundaries of Ogasawara Town, Ogasawara... , 01-10-1944.
  461–473						Cancelled on 11 August 1943.
  5421–5432						Cancelled on 5 May 1944.