Stridsvagn S103 "S Tank" has been out of production - and service - for some time (since the 1990s). Hull-down was never a problem with it's years-ahead-of-it's-time hydraulic suspension. Why would tanks need to keep engines running? - that's what the APU is for, or in the case of the S Tank a combination of petrol engine and turbine engine. Swedish terrain and tactics didn't call for much movement down narrow lanes. Bovington tried the S Tank and liked what they saw... and were surprised by how well the tank did in comparison with other vehicles of the era that were capable of firing on the move. The real end for the concept came with development of truly-effective main-gun stabilisation in turreted tanks.