Clyde Engineering acquired the services of former SAR Chief Mechanical Engineer Fred Shea, to design and oversee the production of a GM-EMD F7 model suitable for use on the Commonwealth Railways system, importantly on the Trans Australia Railway. The equipment was re-arranged to suit Australia's tighter loading gauges, resulting in a lower, longer version of the US EMD unit. The longer carbody facilitated a 3rd, unpowered axle in the bogie, the burden of US axle load being well beyond the tolerance of existing infrastructure.
So impressed was the Commonwealth Railways administration with the locomotive's on-time delivery over 1951/1952, that the fleet was named the GM Class. Design revisions led to the developement of a Co-Co version, the GM-12 Class with an updated EMD power unit. The modifications added a substantial 100kN to the locomotive's continuous tractive effort, and the success of the GM-12 resulted in orders from the Railways of NSW and Victoria.
Over the years, the GM12's could gradually be seen in most mainland states. Due to reciprocal intersystem motive power deals through the 1980s, examples gradually filtered into Perth (WA) and Lithgow (NSW). Others were leased on several extended periods to Victorian Railways (now V/Line) to arrest severe motive power shortages over the Melbourne to Albury standard gauge line while as recently as 1994-95, four at any given time could be found on a rotational basis operating over Westrail's standard gauge Lenora route, again to fill a serious locomotive shortage.
In a surprise eleventh hour move, two dynamic brake units, Nos. GM42 and GM43 were issued to the broad gauge network from March 1992, where they saw diversified service including interstate superfreight train assistance between Adelaide and Tailem Bend, Penrice limestone haulage and Mt Gambier freight workings.
Withdrawls began with No. GM29 late in 1985, the result of a level crossing collision on the Central Australia Railway (Marree line). Gradually others followed and the last two to recieve overhauls were Nos. GM41 and GM44 early in 1995. By then, only nine remained in traffic and, in July 1996, No. GM22 languished at the Port Pirie Railway Museum and No. GM36 had just been bought by the Seymour Loco Steam Preservation Group in Victoria.