• In 1934, the IJN planned an experimental model of a high-speed coast defense submarine chaser. The IJN wanted over 20 kn (23 mph; 37 km/h), however the Navy Technical Department (Kampon) had not designed this type of small craft and the needed high-powered diesel engines yet.
• The IJN ordered the hull design from Thornycroft, and the high-powered diesel design from MAN, to study a small-sized high-speed boat.

• The Thornycroft drawings were not able to satisfy the IJN, because the design's center of gravity was too high, and had bad drainage. Kampon made a hull design based on the Hayabusa class torpedo boat instead.
• The IJN was satisfied with MAN diesel specifications, however their designs were very complicated and very expensive. The IJN bought two engines and labeled them MAN Mk.1 diesel (マ式1号ディーゼル,, Ma-Shiki 1 Gō diesel). Further, the IJN ordered copies of these engines from Kawasaki Heavy Industries and Mitsubishi Heavy Industries.
• Also, 1 vessel was equipped with a Kampon turbine, because the MAN diesel engines were unsuitable for a mass production.

• The IJN deployed them to a mine warfare school after having finished their examination, because they were too small.
• They became a training ship of the mine warfare school, and they acted in Tokyo Bay.

No.251-class edit

• Project number K5A. 2 vessels were completed. They were equipped with MAN design diesels. The No.252 was equipped the copied MAN diesels by Kawasaki and Mitsubishi.

No.251 edit

• 14 December 1936: Laid down as the Submarine Chaser No.51 (第51号駆潜艇,, Dai 51 Gō Kusentei) at Nihon Kōkan, Tsurumi Shipyard.
• 9 June 1937: Launched.
• 30 September 1937: Completed.
• 15 November 1940: Classified to the Auxiliary submarine chaser, and renamed Auxiliary Submarine Chaser No.51 (第51号駆潜特務艇,, Dai 51 Gō Kusen-Tokumutei).
• (after): Assigned to the mine warfare school (Kurihama).
• 30 April 1943: Renamed Auxiliary Submarine Chaser No.251 (第251号駆潜特務艇,, Dai 251 Gō Kusen-Tokumutei).
• 28 August 1944: Classified to the Support vessel (tugboat), and renamed No.1658 (公称第1658号,, Kōshō-Dai 1658 Gō).
• August 1945: The end of war at Uraga, later nothing more was heard.

No.252 edit

• 14 December 1936: Laid down as the Submarine Chaser No.52 (第52号駆潜艇,, Dai 52 Gō Kusentei) at Nihon Kōkan, Tsurumi Shipyard.
• 25 August 1937: Launched.
• 25 July 1939: Completed.
• 15 November 1940: Classified to the Auxiliary submarine chaser, and renamed Auxiliary Submarine Chaser No.52 (第52号駆潜特務艇,, Dai 52 Gō Kusen-Tokumutei).
• (after): Assigned to the mine warfare school (Kurihama).
• 30 April 1943: Renamed Auxiliary Submarine Chaser No.252 (第252号駆潜特務艇,, Dai 252 Gō Kusen-Tokumutei).
• 15 February 1944: Classified to the Support vessel (tugboat), and renamed No.1650 (公称第1650号,, Kōshō-Dai 1650 Gō).
• August 1945: The end of war at Uraga, later nothing more was heard.

No.253-class edit

• Project number K5B. 1 vessels was completed. She was equipped with Kampon turbine. She was classed in the No.251-class in the IJN official documents.

No.253 edit

• 9 January 1937: Laid down as the Submarine Chaser No.53 (第53号駆潜艇,, Dai 53 Gō Kusentei) at Ōsaka Iron Works, Sakurajima Factory.
• 15 July 1937: Launched.
• 31 October 1937: Completed.
• 15 November 1940: Classified to the Auxiliary submarine chaser, and renamed Auxiliary Submarine Chaser No.53 (第53号駆潜特務艇,, Dai 53 Gō Kusen-Tokumutei).
• (after): Assigned to the mine warfare school (Kurihama).
• 30 April 1943: Renamed Auxiliary Submarine Chaser No.253 (第253号駆潜特務艇,, Dai 253 Gō Kusen-Tokumutei).
• 15 February 1944: Classified to the Support vessel (tugboat), and renamed No.1651 (公称第1651号,, Kōshō-Dai 1651 Gō).
• August 1945: The end of war at Uraga.
• August 1946: Sink by unknown effect.

• Ships of the World special issue Vol.45, Escort Vessels of the Imperial Japanese Navy, "Kaijinsha"., (Japan), February 1996
• The Maru Special, Japanese Naval Vessels No.49, Japanese submarine chasers and patrol boats, "Ushio Shobō". (Japan), March 1981