SWS is a hybrid trolleybus prototype that was developed and produced by three Finnish companies Suomen Autoteollisuus (SAT), Wiima and Strömberg in 1979.The Helsinki City Transport (HKL) ordered the prototype to gain experience for the future public transportation strategy for city of Helsinki. The trolleybus got its power from the overhead wires, but for wireless parts it had a diesel generator as a power source.