Although not the very first diesel on the network, 4001 and the 19 classmates that followed wrought the legacy that mattered. A refined version of a classic Alco model, the 40 Class were assembled in Canada by an Alco affiliate, the Montral Locomotive Works, with 4001 and 4002 arriving in Sydney during the spring of 1951.

With traffic booming during the afterglow of World War II, the NSW Railways went on a locomotive shopping spree during the late 1940s and early 1950s, yielding the D58, D59 and AD60 Class steam locomotives for goods traffic. Mixed in there was the historic first order for mainline diesel locomotives: the 20-member 40 Class fleet.

Delivered in pairs over the ensuring six months, the 40 Class was to prove a true game changer. These locomotives could uncouple from a slow, heavy goods train and go straight onto an express passenger service - and excel at both jobs.

Gone was the need for locomotives designed for one task or another. Further, the new 'contraptions' did not require regular servicing, nor coaling and watering, and offered crews a level of comfort that, in the 1950s, was unimaginable when compared to the back-breaking slog of running a steam locomotive.