Sisu S-321, S-322 and S-323 is the first lorry and bus model series made by the Finnish heavy vehicle producer Suomen Autoteollisuus (SAT) in 1932–1934.

Autoteollisuus-Bilindustri made an agreement of equipping lorry Volvo-delivered chassis by locally built cabin and platform.

Some chassis were delivered to Autoteollisuus-Bilindustri but the vehicles were not even started before the company put together its operations with its competitor Autokoritehdas, creating SAT.

Among the first customers were newly founded Oy Alkoholiliike Ab which had ordered two S-322D lorries already in the previous year, as well as a Helsinki firewood distributor, which became an owner of S-321E.

The third production batch included parts made by such Finnish companies as Keskusvalimo, Suomen Gummitehdas, Pietarsaaren Konepaja and Kone ja Silta.

[8] In some cases SAT had to go back to Volvo parts; for example domestically produced track rods turned out to be too weak.

[7] The weakening of Finnish mark against the Swedish crown made importing increasingly unfavourable, forcing SAT to focus more on local sourcing activities.

The content of domestic parts was increased, but they were still powered by Volvo delivered Penta EB engines.

[8] Volvo supplied SAT until autumn 1935; the last delivered components were Timken axles and Ross steering boxes.

[8] Those pre-series units which were based on Volvo LV-66 were powered by six-in-line, OHV type Penta DC engines.

Since the beginning all body panels were produced by SAT although the bonnet and front wings were evidently heavily inspired by those of Volvo.

Vehicles of the pre-series had a larger front wheel bearing cap than the serial produced units.

The strategy proved successful as the Finnish roads, mostly rather harsh back then, put vehicles into test.

The bus turned out to be difficult to sell, as the coach was rather unusual type without aisle and equipped with saloon style side doors.

As the original coach was largely disappeared, the reconstruction work was postponed due to lack of funds, until it was finally done in years 1982–1985.

[8] The first owner was Yhtyneet Paperitehtaat Simpele Paper Mill which sold it in 1939 to Viipuri-based K. Widing Engine Repairs Shop that evacuated the vehicle to Hämeenlinna during the war.

[13] Due to damages the lorry suffered during the war its cabin was later modified and has now a split windscreen and higher roof.