WAGR P and Pr Classes - Background

Background

By the early 1920s the WAGR had obtained only a handful of new locomotive designs since the beginning of the twentieth century and there was a particular lack of large passenger locomotives. The Annual Report of 1920 pointed out the large numbers of obsolete locomotives in service and steadily growing rail traffic, stressing the need for more powerful engines. The most substantial design then in service was the E class 4-6-2s of 1902, of which 65 locomotives had been built for operation in Western Australia and served on a variety of services. Likewise the 20 D class 4-6-4T tank locomotives had helped alleviate pressure on suburban services while the 57 F class 4-8-0s did the same for goods. However, all had been introduced (and subsequently superheated) prior to the First World War, meaning that by the 1920s they were becoming inadequate. At this time the most significant operation requiring new locomotives were the long distance passenger services, particularly on the Perth - Kalgoorlie and Perth - Albany expresses, both of which covered distances in excess of 350 kilometres.

In 1923 approval was given for the construction of ten new superheated pacific type locomotives for operation on heavier mainline rails, suitable for the hauling of the expresses. The locomotives were based on plans drawn up in 1920 under Chief Mechanical Engineer of the WAGR Ernest A. Evans which called for a new design with large diameter driving wheels, a large firebox and a two-wheel trailing wheel for stable operation at speed. The final outline drawings were prepared by E.S. Race in the Midland Railway Workshops and completed in December 1923. Influence for the new P class designs were drawn from both the New Zealand Railways Ab and the Tasmanian R class pacifics.