Sisu S-21

The Sisu S-21 was a prototype heavy truck developed by the Finnish company Suomen Autoteollisuus (SAT) in the late 1950s. It was designed as a heavy-duty vehicle primarily intended for military use, specifically as an artillery tractor.

The S-21 featured a distinctive cab-over-engine (COE) design. It was powered by a Leyland diesel engine, a common choice for heavy vehicles of that era. The truck was designed for all-terrain capability, incorporating features such as all-wheel drive to navigate challenging environments.

While the Sisu S-21 was successfully prototyped and tested, it did not enter mass production. The reasons for this decision likely involved a combination of factors, including cost considerations, changing military requirements, and the availability of alternative solutions. Despite not reaching production, the S-21 contributed to SAT's engineering knowledge and influenced subsequent Sisu truck designs. The prototypes themselves reportedly saw limited use with the Finnish Defence Forces.