Built by A Goninan and Co in Broadmeadow, the six members of the 43 Class visually followed in the footsteps of the streamlined 42 Class, but with internals produced by the American Locomotive Company (ALCo) - a unique combination in any class of Australian diesel locomotive.

With its early diesel orders, the NSW Railways dallied with small orders from a handful of local and overseas builders, before all but settling on a fleet of near-standard Alco mainline diesels over the ensuring decades.

The 43 Class were introduced from 1956 with sights focused on their use on services between Sydney and Orange. With the electrification of the line to Lithgow in 1957 enabling electric-hauled services, the locomotives were transferred to work on the northern routes, taking over services at Gosford and travelling as far as the Queensland Border on both the North Coast and inland Main North routes.