No.31 class patrol boat

No.35 in 1940
Class overview
Name:	No.31-class patrol boat
Builders:	Kure Naval Arsenal Sasebo Naval Arsenal Hakodate Dock Corporation
Operators:	Imperial Japanese Navy People's Security Army
Succeeded by:	Matsu-class destroyer No.1-class landing ship
Subclasses:	No.31-class (ex.-Momi-calss) No.46-class (ex.-Wakatake-class)
Built:	1940
In commission:	1940 – 1946
Planned:	6
Completed:	10
Lost:	9
Retired:	1
General characteristics No.31-class
Type:	Patrol boat
Displacement:	940 long tons (955 t) standard
Length:	April 1940 88.39 m (290 ft 0 in) overall
Beam:	7.93 m (26 ft 0 in)
Propulsion:	2 × geared turbines 2 × Kampon water tube boilers 2 shafts, 4,000 shp
Speed:	18.0 knots (20.7 mph; 33.3 km/h)
Armament:	April 1940 • 2 × 120 mm (4.7 in) L/45 naval guns • 1 × Type 96 25 mm AA gun • 1 × paravane No.32 in 1941 • 2 × 120 mm L/45 naval guns • 2 × Type 96 25 mm AA guns • 2 × depth charge throwers • 18 × depth charges • 1 × landing craft and one companie of Navy Landing Force, or 42 × depth charges
General characteristics No.46
Type:	Patrol boat
Displacement:	925 long tons (940 t) standard
Length:	88.39 m (290 ft 0 in) overall
Beam:	8.08 m (26 ft 6 in)
Propulsion:	2 x Escher Wyss & Cie Zoelly geared turbines 2 × Kampon water tube boilers 2 shafts, 4,000 shp
Speed:	18.0 knots (20.7 mph; 33.3 km/h)
Armament:	• 2 × 120 mm L/45 naval guns

The No.31 class patrol boat (第三十一号型哨戒艇,, Dai Sanjūichi Gō-gata Shōkaitei^?) was a class of patrol boats of the Imperial Japanese Navy (IJN), serving during World War II. 9 vessels were converted from Momi-class destroyer and 1 vessel was converted from Wakatake-class destroyer in 1940.

Background

• In 1939, the IJN was liberated from London Naval Treaty, and they built a lot of Kagerō-class destroyers. On the other hand, aging of the Momi-class destroyers were serious. Their boilers were worn down very much because they were destroyers. Some Momi-class were not able to show 30 knots speed. The Navy General Staff made the Confidential Document No.456. It was an order to rebuilt them into patrol boat about four of Minekaze-class destroyers and six of Momi-class destroyers. The IJN chose nine of Momi-class and one of Wakatake-class. Three Momis and one Wakatake were increased, because two Minekazes were decreased.

Rebuilt

• 10 vessels were sent to dockyards for rebuilt. Q turret, all of torpedo tubes and one boiler were removed in 1940.
• Second half of 1941, the IJN rebuilt them once again for war preparations.^[1] They were rebuilt to the landing craft carrier. Y turret was moved to a place of the Q turret. Furthermore, slope for Daihatsu was installed to their stern, and added deck house for one company of Navy Landing Force. As for the No.31 and the No.46, these rebuilt were not done.

Service

• 10 and 23 December 1941: Sortie for the Battle of Wake Island. (No.32 and No.33)
• 12 December 1941: Sortie for the invasion of Legazpi. (No.34, No.35 and No.36)
• 20 December 1941: Sortie for invasion of Davao. (No.36 and No.37)
• 25 December 1941: Sortie for invasion of Jolo. (No.36 and No.37)
• 11 January 1942: Sortie for the Battle of Tarakan. (No.36, No.37 and No.38)
• 11 January 1942: Sortie for the Battle of Manado. (No.34, No.1 and No.2)
• 31 January 1942: Sortie for the Battle of Ambon. (No.34 and No.39)
• 20 February 1942: Sortie for invasion of Kupang. (No.39, No.1 and No.2)
• 1 March 1942: Sortie for invasion of Surabaya. (No.34, No.36, No.37, No.38 and No.39)
• 31 March 1942: Sortie for the Battle of Christmas Island. (No.34 and No.36)
• (after): The IJN which finished First Phase Operations allotted them to the convoy escort operations. Only No.36 was survived war.

Ships in classes

No.31 class

Ship	Completed as destroyer	Rebuilt completed	Fate
No.31 [2] (ex.-Palau on 30 March 1944. Decommissioned on 10 May 1944.
No.32 (ex.-Battle of Wake Island on 23 December 1941, later scutlled. Decommissioned on 10 January 1942.
No.33 (ex.-Kavieng on 6 March 1943. Decommissioned on 10 January 1945.
No.35 (ex.-Lae on 2 September 1942. Decommissioned on 10 February 1943.
No.36 (ex.-Surabaya. Seized by Indonesian People's Security Army in June 1946, recaptured by Royal Netherlands Navy in July 1946. Decommissioned on 10 August 1946. Scrapped in 1947.
No.37 (ex.-Battle of Balikpapan on 24 January 1942, later scutlled. Decommissioned on 10 April 1942.
No.38 (ex.-Bashi Channel 20°12′N 121°51′E / 20.2°N 121.85°E / 20.2; 121.85 on 25 November 1944. Decommissioned on 10 March 1945.
No.39 (ex.-Yonaguni 23°45′N 122°45′E / 23.75°N 122.75°E / 23.75; 122.75 on 23 April 1943. Decommissioned on 1 July 1943.

No.46 class

No.40 to No.45 were a space to the vessels numbers. These numbers were going to be given to all of Wakatakes.

Ship	Completed as destroyer	Rebuilt completed	Fate
No.46 (ex.-Minamiizu 34°30′N 138°34′E / 34.5°N 138.567°E / 34.5; 138.567 on 10 November 1944. Decommissioned on 10 January 1945.

Photos

• 

  No.46 in 1940 at Kure Naval Arsenal

• 

  No.32 and No.33 at Wake Island (left to right)

• 

  No.33 at Wake Island

• 

  No.31-class in September 1942

• 

  No.31 on 30 March 1944 at Palau

• 

  No.39 on 23 April 1943

See also

• High speed transport
• No.1 class patrol boat
• No.1 class landing ship
• Momi class destroyer
• Wakatake class destroyer
• Battle of Wake Island

Footnotes

1. ^ About the time of their entering a dock, correct historical materials were not left.
2. ^ Patrol boat No.31 (第三十一号哨戒艇, Dai 31 Gō Shōkaitei^?). The same shall apply hereinafter.

Bibliography

• "Rekishi Gunzō". http://rekigun.net/. , History of Pacific War Vol.62 Ships of the Imperial Japanese Forces, Gakken (Japan), January 2008, ISBN 987-4-05-605008-0
• Ships of the World special issue Vol.45, Escort Vessels of the Imperial Japanese Navy, "Kaijinsha". http://www.ships-net.co.jp/. , (Japan), February 1996
• The Maru Special, Japanese Naval Vessels No.49, Japanese submarine chasers and patrol boats, "Ushio Shobō". http://www.kojinsha.co.jp/.  (Japan), March 1981