WAGR P and Pr classes

WAGR P class
P508 at the Western Australian Rail Transport Museum
Type and origin Power type Steam Designer E.S. Race Builder North British Locomotive Company & Midland Railway Workshops Build date 1924-1929 Total produced 25 Rebuilder Midland Railway Workshops Rebuild date 1941-1944 Number rebuilt 8 as Pr class
Specifications Configuration: ​  • Whyte 4-6-2 Gauge 3 ft 6 in (1,067 mm) Driver dia. 4 ft 0 in (1,219 mm) Length 62 ft 2 in (18.95 m) Total weight 102 long tons 5 cwt (229,000 lb or 103.9 t) Fuel type Coal Fuel capacity 7 long tons 0 cwt (15,700 lb or 7.1 t)/ 8 long tons 0 cwt (17,900 lb or 8.1 t) Water cap 2,440 imp gal (11,100 L; 2,930 US gal)/ 2,800 imp gal (13,000 L; 3,400 US gal) Firebox:  • Firegrate area 35 sq ft (3.3 m2) Boiler pressure 160 lbf/in2 (1,100 kPa)
Performance figures Tractive effort 23,638 lbf (105.15 kN) Factor of adh. 3.6
Career Operators Western Australian Government Railways Numbers P441-P465 (as delivered), renumbered P501-P517 in 1947 Last run 1969 Preserved P508 Disposition 1 preserved, 24 scrapped

WAGR Pr class
P521 at the Western Australian Rail Transport Museum, note the running-board nameplate and hemispherical headlight in contrast to the cylindrical example on P508 above
Type and origin Power type Steam Designer E.S. Race Builder Midland Railway Workshops Build date 1938-1944 Total produced 18 including 8 converted from P class
Specifications Configuration: ​  • Whyte 4-6-2 Gauge 3 ft 6 in (1,067 mm) Driver dia. 4 ft 6 in (1,372 mm) Length 62 ft 4 in (19.00 m) Total weight 102 long tons 10 cwt (229,600 lb or 104.1 t) Fuel type Coal Fuel capacity 8 long tons 0 cwt (17,900 lb or 8.1 t) /8 long tons 0 cwt (17,900 lb or 8.1 t) Water cap 2,800 imp gal (13,000 L; 3,400 US gal) Firebox:  • Firegrate area 35 sq ft (3.3 m2) Boiler pressure 175 lbf/in2 (1,210 kPa) Cylinder size 19 in × 26 in (483 mm × 660 mm)
Performance figures Tractive effort 25,855 lbf (115.01 kN) Factor of adh. 3.6
Career Operators Western Australian Government Railways Numbers Pr138-Pr147 (new builds) Pr453-Pr457, Pr459, Pr461, Pr464 (rebuilds) renumbered P521-P538 in 1946 Nicknames River class Last run 1970 Preserved Pr521 Disposition 1 preserved, 17 scrapped

The WAGR P and Pr classes were two classes of 4-6-2 steam locomotives designed for express passenger service on the Western Australian Government Railways mainline network. The initial designs were prepared by E.S. Race and together the two classes had a total build number of thirty-five locomotives, the P and Pr classes entering service in 1924 and 1938 respectively. Both classes were used on express passenger services, greatly improving the economy and speed of long-distance passenger travel in Western Australia, the results of which were most visible on the West Australian stage of the Trans-Australian Railway and Westland Express.

The need for more powerful locomotives in the 1920s resulted in the introduction of twenty-five P class locomotives which provided a significant improvement in power, speed and economy over previous WAGR locomotives, quickly proving to be a highly successful design. The Great Depression of the 1930s, coupled with the effects of the Great War, thwarted the WAGR's later expansion and acquisition plans resulting in many obsolete locomotives remaining in operation into this period. As a result ten new P class locomotives featuring detail improvements to boilers, valves and bogies were introduced in 1938, a year before the outbreak of World War II. The new locomotives became the first WAGR engines to be given names, each bearing that of a prominent West Australian river. These 'River class' locomotives were very successful and proved so invaluable to the operation of the wartime WAGR that eight P class locomotives were modified to their standard. All eighteen locomotives were officially classified as the Pr class in 1946.

The initial ten P class locomotives were built by the North British Locomotive Company in Glasgow while the remainder, including the ten Pr class locomotives, were built locally by the Midland Railway Workshops.

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 to Kalgoorlie and Perth to Albany expresses, both of which covered distances in excess of 350 kilometres.