The WAGR Dm Class was a type of 4-6-4T

4-6-4

Under the Whyte notation for the classification of steam locomotives, 4-6-4 represents the wheel arrangement of four leading wheels on two axles , six powered and coupled driving wheels on three axles, and four trailing wheels on two axles .Other equivalent classifications are:UIC classification:...

 tank engine used by the Western Australian Government Railways

Western Australian Government Railways

Western Australian Government Railways was most common name of the Western Australian government rail transport authority from 1890 to 1976. It is, in its current form, known as the Public Transport Authority of Western Australia....

 from 1945. It was based on the earlier D class

WAGR D Class

The WAGR D Class was a type of 4-6-4T tank engine used by the Western Australian Government Railways from 1912. It was used mostly on suburban passenger workings and was the basis for the later Dm and Dd classes of tank engine which continued this role until the end of steam on WA's Railways....

 but differed significantly in the addition of large boiler-length side tanks, and was built by converting older E Class

WAGR E Class

The WAGR E class were a type of sixty-five steam-locomotives built for the Western Australian Government Railways narrow-gauge network by three British manufacturers Nasmyth, Wilson and Company, Vulcan Foundry, and the North British Locomotive Company, from 1902...

 tender locomotives. The Dm Class served on suburban workings around Perth until the end of steam of Western Australia's railways.

Background

The Second World War was a major setback for Western Australia's railway system. The need to move large numbers of troops and material had taken its toll on the ability of the railways to continue the construction of much needed motive power. During the war years only three new locomotives were built, to the S class

WAGR S Class

The WAGR S Class is a class of 1067mm narrow gauge 4-8-2 Mountain-type steam locomotives built by the Western Australian Government Railways, with construction beginning in 1943...

design, and as much as a quarter of the WAGR's locomotive fleet was out of action pending maintenance. Much of it was over forty years old.