These engines, entered into service with WAGR in 1912, were only the third Garratt design to be produced and represented a significant step in the development of the type.

The second batch, which consisted of seven units, was built in 1913/14 and designated as the Ms class due to the use of superheated steam.

[2][3] All of the M/Ms class locomotives were utilized to haul trains on the WAGR's light lines.

It was reused in the 1970s when the M class diesel locomotives entered service.

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