Initially proposed by the West Australian Government Railway in 1947, the death of the then Chief Mechanical Engineer and some engineering faults in the design delayed their construction until 1951. However, following running in and minor modifications the W Class proved to be a versatile and capable locomotive, with an axle load low enough to allow them onto the entire WAGR network. 

The design of the locomotive takes some cues from Beyer, Peacock & Co.'s Standard Light Garratt. The first 40 were delivered partially erected, whilst the final 20 were fully assembled prior to shipping. The last 20 had larger tenders, capable of holding an additional 2,500 litres.

Beyer, Peacock and Company built 4 additional engines (serial numbers 7418–7419, 7553–7554) to those ordered by the WAGR for the Silverton Tramway Company, Ltd in Broken Hill, NSW.

These locomotives were basically the same as those built for the WAGR, but included a cowling running from in front of the cab to the front of the smokebox. The Silverton locomotives were fitted with Westinghouse Air brakes, and an additional blow-down valve in the middle of the bottom of the boiler barrel.

The Silverton locomotives saw short service with the class being retired in 1961, after Silverton dieselised.