Sisu M-series is a 2–4-axle forward control lorry model series made by the Finnish heavy vehicle producer Suomen Autoteollisuus (SAT) in 1969–1984.

Typical applications were logging trucks, tankers and long-distance transportation haulers which pulled conventional and semi-trailers.

The preceding models of M-series were three-axle KB-112 and two-axle KB-117 which featured a serial produced hydraulically tiltable cabin first in Europe.

[5] In 1968 SAT took over its main domestic competitor Vanajan Autotehdas (VAT) from which it got new technical solutions and the company's new head designer Veikko Muronen.

[7] The first units were handed over to customers already at the end of 1969 but officially the new model was launched in 1970 together with the new R-type, which featured a conventional type cabin.

[4] Already since the 1950s SAT had negotiated with the authorities for allowing four-axle lorries with two steering axles in road transportation.

During the years Leyland had produced for Sisu sturdy, reliable and nearly indestructible engines – as well as technically utterly failed units.

The 315-hp Eagle 320 Mk III presented in 1976 became a famous engine in Sisus; later that year power was increased to 327 hp.

The very last Rolls-Royce engine installed in a Sisu is the Eagle 340 Mk III which was used in the MA-162CZV concept vehicle.

The problem was fixed with silicon carbide treated liners which were taken into use in 1980, after which the engine type became called Rolls-Royce Eagle Mk III "Finlandia."

[5] The producer advertised that the cabin, that contains seats for driver and two passengers, is particularly rigid and fulfilled all the contemporary safety requirements.

Two heaters take care of heating and two fans as well as sunroof are for ventilation; the cabin contains eight nozzles for incoming air.

There are lamps for oil pressure, indicators, alternator charging, differential interlock engagement, air pressure system warning, parking brake engagement and engine overheating indicator, and switches for headlights, heater and ventilation, windscreen wipers, indicators, differential interlock, hand throttle and engine shutdown; the models with tandem axle are also equipped with tandem lifting and lowering switches.

[7] The M-series got several nicknames due to the appearance and characteristics of the cabin; it is commonly known as "rivet-box-Sisu", "showcase-Sisu" and "wiener-booth-Sisu".

[2] The cabins of M-series were used on Sisu-Lokomo mobile cranes and they were also sold to Irish Dennison Truck Mfg.

The voltage of the electrical system is 24 V.[7] The contemporary Finnish legislation allowed a total weight of 16 tonnes for the two-axle M-161.

[18] In 1978 SAT made a study for increasing of payload on logging trucks by reducing the kerb weight.

The trailer was lightened with similar methods, leading to 950 kg lighter kerb weight.

The truck was nicknamed "Emma" and it was developed together with the end customer, company Tehdaspuu Oy.