15) Engineer AFV part 1

Since the early 1930th a number of special vehicles for different tasks were developed and built. Among these a few were used by IJA engineers. These included chargelayers, obstacle removing and mineclearing tanks. The remote controlled vehicles are subject of a later post.

a) Armored Working Vehicle SS:

During the late 1920th the Soviet Union was rated the biggest danger for the japanese plans in East Asia. So with the new development and mobilization plan from 1929 a specialized engineer vehicle able to destroy bunkers and roadblocks should be developed. Design started in 1930 at 2nd Army Technical Bureau based on the technologies gathered during the development of the Experimental Tank No. 2 and the early design stages of the Type 89 Medium Tank. Because of the problematic financial situation instead of just two tasks the vehicle should be able to fulfill several:
- bridge laying
- mine clearing
- obstacle removing
- gas and decontamination agent scattering
- charge laying
- crane operating
- trench digging
- smoke laying
- flame oil throwing

Therefore a versatile and mobile vehicle with several modules for the different tasks was developed. The suspension was similar to the Type 89 Medium Tank with two sets of two pairs of small, bogie connected roadwheels sprung by large packs of leaf springs each. A large driving wheel was at the bow, a large idle wheel in the rear. Four return rollers completed the suspension. The armor was between 6 and 25 mm thick. The frontal armor had a sloped center part, a vertical lower part and an almost vertical upper part. On the left side of the upper armor a large mount for a Type 93 Flamethrower was added. The driver´s visor hatch on the right was openable to the top. The side armor was vertical with the upper part arranged sloped. Diagonal armor plates connected the sides with the bow and rear armor. The rear armor was vertical. A hemispherical commander’s cupola was mounted centered on the forward top armor. The suspension was covered by 6 mm trapezoid armor plates . A large, two-part access hatch in the top armor allowed engine change. The rear engine compartment was accessible from the forward fighting compartment, too. A 105 hp gasoline engine was used which should be replaced by a Diesel engine as soon as possible.

Version Hei with explosive charge mounted on the bow

There were several attachment points on the bow, top and rear. On the bow mine forks plus an obstacle clearing wedge or a 300 kg explosive charge could be added. On the top a crane, smoke agent canisters and/or two different types of bridges (7 m and 10 m scissor type) could be carried. On the rear a fluid tank for chemical agents or flame oil or a large trench plough could be attached. The chemical agents could be dispersed by a spray nozzle attachable inside the flame thrower mount. The vehicle was able to fulfill all demanded tasks but not at the same time as some modules couldn´t be used parallel.

First operational tests started in 1933. In 1934 two vehicles were send to China to be tested at 1st Mobile Brigade. Due to the available space inside the vehicle the new Type 94 Model 4 radio set was added in 1935. Several necessary changes and a low priority delayed official introduction until 1936. As this vehicle was developed for engineer units which were not allowed to operate “tanks” the designation “Soko Sagyosha” = “Armored Working Vehicle” was chosen, short designation “SS”.

There were five versions during the years:

Version Kou(A) = A:

Basic production version with a 140 hp gasoline engine. 13 were built.

Version Otsu = B

Version Otsu had a modified suspension with one return roller removed, and modified Driving and idle wheels. The vehicle seemed to be specialised to flame throwing. Four small, armored flame oil tanks were mounted fixed between the suspension parts. Due to the tanks the suspension armor could not be used any more. A concrete made flame oil tank was added to the rear. An additional flame thrower mount was implemented in the remodeled forward side armor. In addition the bow armor was remodeled similar to the Type 89 tank with a sloped lower part and a vertical upper part.
The commander´s cupola was now quadratic with sloped sides and a two-part hatch on top. 8 vehicles were built

Version Hei = C

Version C was a remodeled Version A. The suspension also had three return rollers and modified driving and idle wheels but the flame oil tanks were not used. The suspension armor consisted of several welded armor plates instead of a harder to produce single plate. The two additional flamethrower mounts were placed in the forward side armor. The commander´s cupola was hemispherical again. The now used Mitsubishi I6 Diesel engine with 145 hp at 1800 rpm allowed a maximum speed of 37 km/h. 1 vehicle was built

Version Tei = D

Version D was a remodeled version B. Driving wheels and idle wheels were modified again to spare weight. The shape of the driver´s hatch and the bow flamethrower port were modified and a standard MG mount for a Type 97 7,7 mm MG was added between them for better close defense. The Type 93 flamethrowers were later replaced by the lighter Type 100 Flamethrowers. The commander´s cupola was now conical. And the Diesel engine was used. 20 vehicles were built.

Version Bo = E

Modified version D. The suspension was simplified by removing another return roller and the armor plate wasn´t used any more but suspension side armor was increased to 13 mm. The commander´s cupola was now cylindrical. Armament consisted of three standard infantry Type 100 Flamethrowers and a Type 97 7,7 mm MG. 77 vehicles were built.

The need to exchange the modules for different tasks finally leads to the decision to develop special purpose-built vehicles as replacement around 1940. None of these developments was introduced. They will be covered in a different post. Several Independent Engineer units and after 1942 especially the tank division engineers were equipped with the SS.


vehicles built: 119
weight: Kou(a) 9,6 (metric) t , Otsu 9,8 t, Bo 13 t
crew: 5 men
length: 4865 mm
width: 2520 mm
height: 1800 mm
armor: 6 – 25 mm
engine: Kou(A) 120 hp gasoline, Hei 145 hp Diesel
maximum speed: 37 km/h on roads
armament: 1 – 3 X Type 93, later Type 100 Flamethrower; 1 X Type 97 7,7 mm MG for Hei and Bo

to becontinued in part 2...