| Weight | 109t 1cwt |
| Driving Wheels | 4ft 6in |
| Boiler Pressure | 175psi |
| Cylinders | Outside – 19in x 26in |
| Tractive Effort | 25,855lbf |
| Valve Gear | Walschaerts |
After the Second World War the Western Australian Government Railways (WAGR) was short of motive power which resulted in an authorisation being given for the procurement of 35 4-6-2 locomotives. It was initially planned that 10 of these would be built at the Midland Railway Worksops and 10 being constructed externally. Due to capacity constraints at Midland an order for 35 locomotives was placed with the North British Locomotive Company in Glasgow and these became the Pm class.
Nineteen were built as the Pm class with plain bearings on the coupled axles and roller bearings on the carrying axles. The other sixteen were built as the Pmr class with roller bearings on all axles. One Pm was later converted to a Pmr at the Midland Railway Workshops.
All of the 35 locomotives entered service on the WAGR in 1950.
Although they were designed to operate passenger services, their independently sprung driving wheels gave a rough ride meaning they could not maintain schedules, hence they were quickly relegated to fast freight trains on the Eastern Goldfields and Great Southern lines and associated branches. They were restricted to a maximum speed of 40mph.
Later they were concentrated on the Great Southern and South Western lines.
All of the locomotives were withdrawn from service between 1970 and 1972. This locomotive (701) was withdrawn from service in 1971.
There are five other Pm/Pmr locomotives built by the North British Locomotive Company that have been preserved.
- Pm 706 – Works number 26550
- Pmr 720 – Works number 26564
- Pmr 721 – Works number 26565
- Pmr 729 – Works number 26924
- Pmr 735 – Works number 26930
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Preserved British Steam Locomotives 