The class were ordered as light goods locomotives for use on the expanding South Australian Railways 3 ft 6 in (1,067 mm) gauge lines, necessarily limited in size and weight by the lightweight 40 lb/yd rails used at the time.

Early W class units were used during construction of the Central Australia Railway between Port Augusta and Quorn in 1878 before entering revenue service with SAR.

[2] Several of the locomotives were sold to C&E Millar and used for construction of the Palmerston and Pine Creek Railway in the Northern Territory and would continue to work the isolated line for the remainder of their operational lives.

[3] From 1903, the SAR began to rebuild W class locomotives with upgraded boilers increased to 145 psi (1,000 kPa) pressure, which improved the tractive effort to 8,566 lbf (38.10 kN).

Several Wx class units were also withdrawn in 1929, but a small number endured until 1959[3] when the SAR's South-eastern Division narrow-gauge lines were converted to 1600 mm (5 ft 3 in).