The class was preceded on the WAGR system by the M and the Ms Garratts. The class were used extensively on WAGR lines with light rails and sharp curves, as a consequence many of the smaller older branch lines on the Darling Scarp; as well as those with steep inclines such as those on the Mundaring Weir Branch Railway, the Nannup Branch, and the Flinders Bay Branch Railway railways.
Hearsay evidence suggests that the poor quality of the boilers in the Msa rendered some inoperable by the late 1940s. The last remaining Msa was awaiting moving to a preservation status in the 'steam graveyard' adjacent to the Midland Railway Workshops, when instructions were misunderstood by a scrap metal company employee, and it was destroyed.
Watson, Lindsay (1995) The Railway History Of Midland Junction : Commemorating The Centenary Of Midland Junction, 1895-1995 Swan View, W.A : L & S Drafting in association with the Shire of Swan and the Western Australian Light Railway Preservation Association.
Gunzburg, Adrian.(1984) A history of W.A.G.R. steam locomotives Perth, W.A : Australian Railway Historical Society, Western Australian Division. ISBN 0959969039