[1][2][3][4] These 4-6-4 tank locomotives were specifically designed to haul Sydney's ever increasing suburban traffic, particularly over the heavy grades on the Northern, North Shore and Illawarra lines.

[5] The inner-city lines' electrification made the locomotives obsolete, but they were too valuable to be withdrawn and scrapped at the time.

[2][6] The remaining unaltered locomotives were primarily utilized on Sydney suburban services to Cowan, Penrith, and Campbelltown, as well as branches to Carlingford, Richmond, and Camden.

[6] A few drifted to the country areas, working on sections where no turntable was readily available, such as Casino to Border Loop on the North Coast line, Leeton and Merriwa, and shunting at yards such as Bathurst.

Until February 1967, these locomotives operated the daily passenger trains on extremely steep Unanderra to Moss Vale line.