The S636-class 4-6-4 steam locomotive was introduced in the Australian State of New South Wales (NSW) by the Government Railways in 1903. 145 locomotives were built. The locomotive was renumbered to the 30 class in 1924.
Originally saturated tank engines, in 1928 half were converted to tender engines, with boiler pressure increased by 15 psi and two dozen or so were fitted with superheating, improving performance.
The last locomotive was withdrawn from service in 1965.
Several preserved loco's survive today, at least one is in operational condition.