(left to right) No. 1, No. 2 and No. 3 in 1938
Class overview
Name	No. 1-class submarine chasers No. 1 class (Project number K3) No. 3 class (Project number K4)
Builders	Uraga Dock Company Tōkyō Ishikawajima Shipyard Asano Shipyard
Operators	Imperial Japanese Navy
Succeeded by	No. 4 class
Cost	1,525,700 JPY (No. 1-class) 1,530,000 JPY (No. 3-class)
Built	1933 – 1936
In commission	1934 – 1946
Planned	3
Completed	3
Lost	1
Retired	2
General characteristics No. 1-class
Displacement	266 long tons (270 t) standard 280 long tons (284 t) trial and after late 1934 377 long tons (383 t) trial
Length	65.30 m (214 ft 3 in) overall 64.00 m (210 ft 0 in) waterline
Beam	5.90 m (19 ft 4 in)
Draught	1.43 m (4 ft 8 in)
Propulsion	2 × Kampon Mk.22 Model 8 diesels 2 shafts, 3,400 bhp
Speed	24.0 knots (27.6 mph; 44.4 km/h) and after late 1934 21.1 knots (24.3 mph; 39.1 km/h)
Range	1,500 nmi (2,800 km) at 14 kn (16 mph; 26 km/h)
Complement	65
Armament	2 × 40 mm heavy machine guns 36 × depth charges 1 × depth charge thrower 1 × Type 93 active sonar 1 × MV hydrophone
General characteristics No. 3-class
Displacement	270 long tons (274 t) standard 285 long tons (290 t) trial
Length	56.10 m (184 ft 1 in) overall 55.00 m (180 ft 5 in) waterline
Beam	5.60 m (18 ft 4 in)
Draught	2.10 m (6 ft 11 in)
Propulsion	2 × Kampon Mk.22 Model 6 diesels 2 shafts, 2,500 bhp
Speed	20.0 knots (23.0 mph; 37.0 km/h)
Range	1,500 nmi (2,800 km) at 14 kn (16 mph; 26 km/h)
Complement	60
Armament	2 × 40 mm heavy machine guns 36 × depth charges 2 × Type 94 depth charge projectors 1 × depth charge thrower 1 × French SCAM active sonar 1 × Type 93 hydrophone

The No. 1-class submarine chaser (第一号型駆潜艇, Dai 1 Gō-gata Kusentei) was a class of submarine chasers of the Imperial Japanese Navy (IJN), serving during World War II. Three vessels were built in 1933-36 under the Maru 1 Programme and the Maru 2 Programme. They have two sub classes.

Background

• In World War I, German U-boat raged. The IJN began maintenance of an anti-submarine boat as a lesson in this, because Japanese shoreline and sea-lanes were very long. The IJN had some submarine chaser type tugboats and yard ferries. However, they were small and their speed was low.
• The IJN wanted to give the anti-submarine boats a speed of more than 20 knots, because their Kaidai III submarine already achieved a 20kt surfaced.

Design

• The Naval Technical Department (Kampon) made draft shallow to give them high speed. They achieved 24 kt speed hereby.
• The No. 1 and the No. 2 were completed in March 1934, and they were assigned to the 1st Submarine Chaser Division, Yokosuka Naval Defence Squadron.
• However, because of their very shallow draft they lacked the rolling performance. This fact become evident after the Tomozuru incident.
• The Tomozuru incident affected the No. 1-class. The No. 1 and the No. 2 were sent to the Uraga Dock Company in July 1934, and repairs were started. They were equipped 80 tons ballast and mounted a ballast keel. The drawings for the No. 3-class boat was also revised.

Service

• Late 1934, Repairs were completed.
• October 1936, The No. 3 assigned to 1st SchDiv. They always shared an action afterward.
• In 1938, the 1st SchDiv was transferred to the No. 1 Base Force (Shanghai).
• On 5 September 1941, the No. 1 Base Force was transferred to the 2nd Fleet.
• In December 1941 – March 1942, the 1st SchDiv engaged to the Battle of the Philippines and Dutch East Indies campaign.
• On 10 March 1942, the 1st SchDiv was transferred to the No. 21 Special Base Force (Surabaya), 2nd Southern Expeditionary Fleet, Southwest Area Fleet.
• On 1 May 1942: The 1st SchDiv was dissolved. They spent all their time for escort operations in the Java Area.

Ships in classes

No.1-class

• Project number was K3. 2 vessels were built under the Maru 1 Programme. They equipped the MV hydrophone by Submarine signal company and latest active sonar the Type 93.

No.3-class

• Project number was K4. Only 1 vessel was built under the Maru 2 Programme. The No. 3 was equipped the French SCAM active sonar and latest hydrophone the Type 93. The No. 3 was classed in the No. 1-class in the IJN official documents.

Photos

• 
  No. 2 in 1934
• 
  No. 3 in 1936