The S class loco's were built in two batches. Numbers 300 - 309 were built by Clyde Engineering 1957/58. Numbers 310 - 317 were built 1960/61 for standard gauge service.
Speed on the VR was 70mph (115km/hr). They were an 1800hp locomotive, with C-C ( Co-Co ) bogies.
They were used for main line service running freights and passenger trains.
S 314 and S 316 were written off in 1969 after a collision.
S 317 was rebuilt twice; once after a collision in 1969 and again after a collision in 1981.