The design is based on the Electro-Motive Diesel EMD F9 locomotive, and is very similar to the GM 12 class then being built by Clyde Engineering for the Commonwealth Railways.

[1][2] As newer locomotives arrived they were concentrated on the Main South line operating freight services.

By April 1978, the Goulburn branch of the Australian Federated Union of Locomotive Enginemen had placed a ban on operating the 42 class as lead engines due to cab conditions.

In 1980, to overcome those problems, 4201 had its cab upgraded during an overhaul but, with their replacement imminent, it was decided not to modify the rest of the class.

A fourth was preserved, but this has since been mostly cut up: Media related to New South Wales 42 class locomotives at Wikimedia Commons