The 73 class is a diesel-hydraulic locomotive built by Walkers Limited, Maryborough for the New South Wales Department of Railways between 1970 and 1973.

The New South Wales Department of Railways placed an order in October 1969 with Walkers Limited, Maryborough for 20 B-B shunting locomotives.

When the whole of the first order had arrived, all steam shunting on the North Coast line and the Sydney Metropolitan area, as well as at Goulburn had been replaced.

[1] The New South Wales Department of Railways purchased the class mainly for shunting and their prohibition from mainline use was 'officially' due to the lack of vigilance controls.

[3] As an example of the spread of the members of the class throughout the system, the fleet was allocated as follows as at 30 August 1977: With a reduction in locomotive hauled passenger trains and the closure of a number of yards, withdrawals began in February 1987.