IJA Small Escort Boat (Se-Ha Kai)

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小護衛艇(せは艇改) / Small Escort Boat (Se-Ha Kai)


Briefly: Reinforced Ha-Go fighting boat with 6x 20mm autocannons!


  • Combat boat / 戦闘用舟艇
    • Escort boat / 護衛艇

Historical background

Small escort boat (project name: Se-Ha Kai) was Japanese army’s gun boat project in late of war.

In the late of pacific war, Japanese need small escort vessel to defend transport boats (Daihatsu landing craft, Motorsailer etc.). In that time they have “Soukou-Tei” (AB), but it have complex structure so it production is not enough. To solve this problem, they planed a small escort boat which is able to built small civilian shipbuilders.

At first, they planned two designs with different engines. Model 1 had two 150HP engine and Model 2 had two 60HP engines.

Ha-Go Fighting Boat Model 2, also called "Se-Ni launched October 1944. As a result of trial, speed of this boat was only 9 knots in spite of Army required that speed of escort boat should be over 12 knots. The plan was abandoned because the performance was significantly inferior to the requirements and was considered difficult to resolve.

Ha-Go Fighting Boat Model 1, also called “Se-Ha” launched December 1944 and engineers tested it during Dec 21 to 23. As a result of it, they select model 1 but they find that to modify hull and it will get more good speed.

In the second stage, engineers build new prototype: Se-Ha Kai. It was launched July 1945, and tested during August 2-5. In this trial test, speed of Se-Ha Kai reached 13 knot.

As a result of it, Japanese army adopted this weapon as “Small Escort Boat” (小護衛艇). However, just after adopted it, war was ended so it was not mass-produced.


Ship hull is ordinally V-type displacement ship, but designer used lots of straight line to reduce costs. Outboard is thin steel (all welding), and use large stringer.

Protection was limited that only steering room had armor.

Main weapon is Type 4 20 mm twin machine gun “So-Ki”, a shipborne variant of Type 98 20 mm machine gun. Different to first prototype “Se-Ha”, it have three mount of 20 mm twin gun instead of useless 57 mm cannon. In addition it had army’s domestic design sonar and depth charges.

Interestingly, this boat have cooking equipment using engine engine exhaust. This machine able to cook two rice bowl in 20 minutes by one engine.


  1. Rigging storage
  2. Crew chamber
  3. Ammunition box storage
  4. Steering room
  5. Engine room
  6. Ammo and depth charge storage
  7. Warehouse
  8. Fuel tank
  9. Fuel tank
  10. Main engine
  11. Fuel tank
  12. 1st stage ammo racks
  13. 20 mm twin AA cannons
  14. 1st stage ammo racks
  15. Command section
  16. Handrail
  17. Ventilation tube
  18. Depth charge lifting device
  19. Depth charge dropper
  20. Couch
  21. Depth charge
  22. Ra-Go device (sonar)


Type 4 130HP Diesel Engine


Length 23.000 m
Width 3.500 m
Depth 1.800 m
Full load displacement 28.870 t
Draft (bow) 0.661 m
Draft (stern) 1.192 m
Draft (average) 0.927 m
Speed (full load) 13 kt (24 km/h)
Cruise range 100 hours
Engine 2x Type 4 130HP diesel engine
Max power 150HP/1,500 rpm
Weapon 3x Type 4 cylinder-mount Twin 20mm AAG
6x Depth charge (two racks)
1x Ship radio Ko
1x Vehicle radio Hei
1x Ra-Go sonar


For War Thunder, this boat will be good addition for Japanese coastal tree as an upgrade of Ha-Go fighting boat.

Speed is not a good, but six 20 mm machine guns are deadly for small boats and slow attack aircrafts so it is very good gun boat for players.


No.10 Army technical research institute (July 25, 1945) “Small Escort Boat Trial Plan”

No.10 Army technical research institute (November 11, 1944) "Experimental 130HP diesel engine research report)
flame number 104-112

Fujita Masao (2008) "Unknown records of ‘Army Shipping Units [2]’ " Maru, 61(5): 120

Okumoto Gou (2016) “Boats and Ships of Japanese Army: For Landing, Transporting, Escort, Attack and special ships”, Dai-Nippon Kaiga publishers
ISBN: 978-4-499-23177-0 C0076



Pretty interesting +1

This would be deadly as a coastal gunboat. +1 for sure.

Insane firepower for such a small boat +1

Must put it in tank TT than Coastal.