Sōkō Sagyō Ki

The Sōkō Sagyō Ki (装甲作業機), also known as the SS-Ki (SS機/SS器), was a fulltrack engineering vehicle of the Imperial Japanese Army introduced in the 1930s. The vehicle was considered by the IJA as one of its most versatile multi-function support vehicles.

History
During the 1930s, the Imperial Japanese Army required a specialised vehicle in preparation for war against the Soviet Union, which was capable of destroying Soviet fortified positions along the Manchurian border. During the development planning, the capabilities of the vehicle were decided to include trench digging, mine clearing, barbed wire cutting, mass decontamination, spreading poisonous gas, use as a crane vehicle, as a flamethrower tank, and able to lay temporary bridges.

The first prototype was built in 1931. Following testing, the Imperial Japanese Army ordered several vehicles, with the first four assigned to the 1st Mixed Tank Brigade sent to China. During the Battle of Beiping–Tianjin, the vehicles were used as flamethrower tanks, however for the battles after the vehicles were exclusively used as engineering vehicles. They were eventually sent to the Soviet-Manchurian border within an engineer regiment.

During December 1941, approximately 20 vehicles were transferred to the Philippines as part of the 2nd Tank Regiment until the end of the war. 8 vehicles were captured by the United States military during the summer of 1945, who mistakenly classified the vehicles as flamethrower tanks.

Design
Whilst the design featured remnants of the Type 89 I-Go tank design and used a few of its parts, it also featured other parts from various mass-production vehicles. The suspension was made from two blocks of four roadwheels with two return rollers and no independent forward bogie, in addition to semi-elliptical leaf springs. The steering sprocket was placed within the front of the vehicle, whilst the drive sprocket was placed within the rear. The vehicle weighed 13 tons and fitted five crewmembers.

The first vehicles had a hull based on the Type 94, with modifications to the driver's hatch and the addition of flamethrowers. The turret was removed and replaced with a small commander copula with fitted observational devices; two claws used for mine clearing were placed in the front, while a winch designed to pull heavy objects was placed in the rear, and was directly powered by the engine. The thickness of the armor was reduced to 6mm on the roof and bottom, 13mm at the sides, and 25mm at the front, since the vehicle was not intended for combat at the front lines.

A Mitsubishi I6 diesel engine was used, which provided 145 horsepower at 1800 rpm, allowing the vehicle to travel at a top speed of 37kph; this was in conjunction with a mechanical transmission.

Variants
Up until 1943, 119 of these vehicles were built within six variants:
 * SS Ki: Main variant
 * SS Kou Gata (甲型): Armored engineering vehicle with suspension tracks consisting of four return rollers
 * SS Otsu Gata (乙型): Armored bridgelaying vehicle with three return rollers and modified drive sprockets
 * SS Hei Gata (丙型): Armored trench digger with identical suspension as the Otsu Gata, with additional armor plates
 * SS Tei Gata (丁型): Armored engineering vehicle with identical suspension as the Otsu Gata
 * SS Bo Gata (戊型): Armored bridgelaying vehicle based on the design of the SS Ki