[1] In 1900, Victorian Railways still ran express passenger trains with the successful but ageing B class 2-4-0 which dated back to 1862.

[2][3] Innovative design features of the AA class included air sanding equipment, improved Gresham No.

9 injectors, horizontal grid spark arrestors, steam for auxiliaries supplied directly from the dome, and a sloped ashpan to provide easier cleaning.

422 demonstrated considerably greater efficiency and reduced maintenance, and the AA became the first of many subsequent VR locomotive classes to be built with piston valves.

[2] With an axle load of 16.85 long tons (17.12 t; 18.87 short tons), the AA had reached the design limits of size and power possible with a two-coupled axle locomotive type with Victoria's relatively lightweight track infrastructure.

However, the AA continued in service in assistant duties, as well as hauling show and race train specials.

[6][9] They were all scrapped shortly after withdrawal, with the exception of Newport Workshops boiler locomotive AA 532, which lasted until 1940.