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	Auxiliary Submarine Chaser No.251 in 1938
Class overview
Name	No.251-class aux. submarine chasers; No.251-class (Project number K5A); No.253-class (Project number K5B);
Builders	Nihon Kōkan Corporation; Ōsaka Iron Works;
Operators	Imperial Japanese Navy
Built	1936 – 1939
In commission	1937 – 1945
Planned	3
Completed	3
Retired	3
	Auxiliary Submarine Chaser No.253 in 1937
General characteristics
Type	Submarine chaser
Displacement	170 long tons (173 t) standard
Length	45.0 m (147 ft 8 in) overall
Beam	4.80 m (15 ft 9 in)
Draught	No.251 and No.252; 1.70 m (5 ft 7 in); No.253; 1.73 m (5 ft 8 in);
Propulsion	No.251; 2 × original MAN Mk.1 diesels; 2 shafts, 3,000 bhp; No.252; 2 × copied MAN Mk.1 diesels; 2 shafts; No.253; 1 × Kampon geared turbine; 2 × Kampon water tube boilers; 2 shafts, 3,000 shp;
Speed	23.0 knots (26.5 mph; 42.6 km/h)
Range	800 nmi (1,500 km) at 14 kn (16 mph; 26 km/h)
Complement	41
Armament	1 × 40 mm heavy machine gun; 18 × Type 95 depth charges; 2 × Type 94 depth charge projectors; 1 × depth charge rack; 1 × Type 93 active sonar; 1 × Type 93 hydrophone;

The No.251 class auxiliary submarine chaser (第二百五十一号型駆潜特務艇,, Dai 251 Gō-gata Kusen-Tokumutei)^[1] was a class of submarine chasers of the Imperial Japanese Navy (IJN), serving during World War II. 3 vessels were built in 1936 – 1939 under the Maru 2 Programme. They have two subclasses, this article handles them collectively.

Background

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.

Design

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.

Service

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.

Ships in classes

No.251-class

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

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

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

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

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.

Footnotes

^ At first No.51 class submarine chaser (第五十一号型駆潜艇,, Dai 51 Gō-gata Kusentei), until 15 November 1940.

Bibliography

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