Explosive motorboats

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Explosive motorboats

Post by Tanaka »

The imperial Japanese Army's Warship research institute was directed in March 1944 to develope ''Special (attack) boats''. One month later the Japanese Navy issued a similiar directive to its own departments of Warship and aircraft productions. It is safe to say though that the Japanese had been considering the use of suicide weapons since 1943, and that the orders issued in 1944 were merely an official sanction for there developement, since the first units equipped with these weapons were being deployed for operations just 5 months later in August-September 1944.

The Imperial Japanese Army's interest in explosive motor boats came about by the inability of its airforce to strike effectively at the most vulnerable elelments of the Allies amphibious landing forces, the transport and troop landing ships.

The IJA adopted the Maru-ni (capacious boat) as a method of attacking the troop transports as they lay off the beaches at night. The name Maru-ni demonstrates the army's reluctance to commit to an openly suicidal weapon. They were also known as Renraku-tei (''Communications boat'')
The Navy was more happy to acknowledge the true nature of the boats by naming there version a Shinyo (''Ocean shakers'' or ''Sea-Quake'').

The Army greatly increased its interests in suicide tactics after the fall of Saipan in June 1944. The Army's airforce was ordered to focus on the troop transports, ignoring the escort ships and to attack with low level skip bombing or if necessary suicide dives.
The Maru-ni were to strike at transport ships at anchor.

The Navy's interest in suicide craft stemmed largely from there neglect of conventional Motor Torpedoe boats in the pre war years and there inability to develope during the war a small fast attack boat similiar to the US Navy's PT-boats.


Length:- 18ft
Engine:- Rebuilt automobile engine
Power:- 80shp
Speed:- 25-30kt
Armament:- one 441lb depthcharge or two smaller charges

On paper the Maru-ni was not a suicide weapon. The Army manual stated the method of attack was to make a high speed run on the target, release the depthcharge alongside the target, fuzed to detonate in about 4 seconds and then head away before detonation. In reality the pilot had little chance of surviving such an attack. Former members of EMB units say most pilots decieded to try and ensure a hit by ramming there targets.

The Army did make an attempt at making a high speed version of the Maru-ni by fitting the Type N-1 with booster rockets which would be used on the last few hundreds yards of an attack. In late 1944 in Hiroshima, tests with these rocket assisted boats achieved speeds of 50-60kt over short distances.
Only two or three of these boats were ever built so were obviously deemed unsuitable for actually combat.


Type 1

-Material: Steel, wood
-Length: 6 meters
-Width: 1,67 meter
-Water displacement: 1,35 tonnes
-Max. speed: 26 knots
-Total engines: 1
-HP: 67
-Fuel tank: 140 liters
-effective range: 250 miles
-Crew: 1

Type 1/1

-Material: wood
-Length: 5,10 meters
-Width: 1,67 meter
-Water displacement: 2,40 tonnes
-Max. speed: 23 knots
-Total engines: 1
-HP: 67
-Fuel tank: 140 liters
-effective range: 250 miles
-Crew: 1

Type 5

-Material: wood
-Length: 6,50 meters
-Width: 1,86 meter
-Water displacement: 1,40 tonnes
-Max. speed: 25 knots
-Total engines: 2
-HP: 134
-Fuel tank: 280 liters
-effective range: 275 miles
-Crew: 2

Type 8

-Material: Wood
-Length: 8 meters
-Width: 2,50 meter
-Water displacement: 4,00 tonnes
-Max. speed: 22 knots
-Total engines: 3
-HP: 200
-Fuel tank: 600 liters
-effective range: 350 miles
-Crew: 3

The Shinyo's warhead was a 551lb-661lb (250-300kg) explosive charge. Most boats had this charge rigged to explode on impact, the crushing of the boats bow completed a simple electrical circuit. Later models sometimes had a switch in the cockpit which could be used to detonate the warhead, this in effect turned the boats pilot into a human bomb.
Most of the boats built after January 1945 were fitted with 2 RAK-12 rocket guns. These were simple crude wooden projectors mounted to either side of the cockpit. Each projector could fire a single 4.7in projectile weighing 49.5lb, intended to be fired at close liberating a shot gun scatter of metal slugs. The intended target would be the lightly armoured positions of the target ships 20mm and 40mm gun positions.

A shinyo squadron consisted of 40-50 boats. One boat in that squadron was crewed by two men, the squadron commander and his pilot. The idea being that the commander would bring up the rear of a mass sortie and observe the squadrons attacks, if needed he could provide covering fire from the machine gun fitted just infront of the cockpit on a swivel mount. The type 93 HMG was specified to be fitted to the Type 1/Improved 4 and the larger Type 5 boats.
After seeing all the men in the squadron strike he would order his pilot to attack and both men would die together.




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