Sisu S-21 is a lorry first produced by the Finnish heavy vehicle producer Suomen Autoteollisuus (SAT), then under names Sisu S-22 and S-22K by Yhteissisu, which, after changing its name Vanajan Autotehdas (VAT), produced it with name Vanaja V-48. The production period was 1943–1955. The two-axle, 4×2-driven lorry has a kerb weight of 3 000 kg and gross weight of 7 000–8 000 kg, depending on version. VAT replaced the model by 1951 presented Vanaja VK-series; in the meantime, SAT developed its follower named .