Contents

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 class) 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 × 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 boats (第三十一号型哨戒艇,, Dai Sanjūichi Gō-gata Shōkaitei) were a class of patrol boats of the Imperial Japanese Navy (IJN), serving during World War II. 9 vessels were converted from Momi-class destroyers and 1 vessel was converted from a Wakatake-class destroyer in 1940. During WW2 all were lost except one.

In 1939, the IJN was liberated from London Naval Treaty, and they built many Kagerō-class destroyers. On the other hand, aging of the Momi-class destroyers was serious. Their boilers were degraded due to the operating conditions present in destroyers. Some Momi-class destroyers were not able to show 30 knots speed. The Navy General Staff made the Confidential Document No. 456. It was an order to rebuild them into patrol boats - about four Minekaze-class destroyers and six Momi-class destroyers. The IJN chose nine Momi class and one Wakatake class. Three Momis and one Wakatake were increased, because two Minekazes were decreased.

• Ten vessels were sent to dockyards for rebuilding. "Q" turret, all of torpedo tubes and one boiler were removed in 1940.
• In the second half of 1941, the IJN rebuilt them once again for war preparations.^[1] They were rebuilt to the landing craft carrier. The Y turret was moved to a place of the "Q" turret. Furthermore, a slope for Daihatsu-class landing craft 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, those rebuilt were not done.

• 10 and 23 December 1941: Sortie for the Battle of Wake Island. (No. 32 and No. 33) (both were lost in Battle of Wake Island)
• 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.

No 36 was the only one to survive the WW2.

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

• 
  No. 31-class in September 1942
• 
  No. 31 on 30 March 1944 at Palau
• 
  No. 32 and No. 33 at Wake Island (left to right)
• 
  No. 33 at Wake Island
• 
  No. 39 on 23 April 1943
• 
  No. 46 in 1940 at Kure Naval Arsenal

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

• "Rekishi Gunzō"., History of Pacific War Vol.62 Ships of the Imperial Japanese Forces, Gakken (Japan), January 2008, ISBN 978-4-05-605008-0
• 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