The S Class locomotives were designed as an express locomotive for the route between Murray Bridge and the border with Victoria. The first 12 were delivered by James Martin & Co in 1894, followed by a further six in 1903/04. They type was notably used to haul the Melbourne Express. The S class had 6'6" driving wheels, the largest of any Australian locomotive, to give it high speeds on low grades.
The engines were pushed out of main line service in the 1920s by 600 class locomotives and Brill railcars. They continued to serve on secondary services into the 1950s. Some locomotives even served in shunting duties despite being unsuitable due to their large wheel diameter. The last examples were retired in 1961.