New South Wales 73 class locomotive
Candy coloured 7318 shunts Grafton yard in January 1986
In October 1969 the New South Wales Government Railways placed an order in October 1969 with Walkers Limited, Maryborough for 20 Bo-Bo shunting locomotives. These were the only New South Wales locomotives to be built in Queensland.
The first unit was delivered in October 1970. 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. In July 1971 a further 30 units were ordered. The last of these arrived in March 1973 and this brought to an end all remaining steam shunting operations in New South Wales.
The New South Wales Government Railways purchased the class mainly for shunting and their prohibition from mainline use was 'officially' due to the lack of vigilance controls. However, despite its absence, the class was still seen on many suburban trip workings and when mainline operation was a necessity, there seemed to be no hesitation to use them.
One advantage a diesel-hydraulic locomotive has over a diesel-electric variety is its ability to negotiate up to 300mm of water over the tracks. Big floods in March 1976 gave 7323 an opportunity to show off its swimming ability when water covered the line near Bourke and this locomotive was used on a couple of freight trains and a ballast train from Nyngan to Bourke and return. At least two other occasions when their water resistance was put to use was Menindee in 1976 and Hexham in 1977.
Multiple unit operation was common, although the flood event at Hexham is the only known occurrence of triple-heading. A number of units were fitted with exhaust gas scrubbers for use on Eastern Suburbs Railway construction in the 1970s.
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:
|Eveleigh||7301–7314, 7317, 7321, 7339–7345|
|Junee||7320 (actually working at Albury)|
|Werris Creek||7346 (actually working at West Tamworth), 7347|
With a reduction in locomotive hauled passenger trains and the closure of a number of yards, withdrawals began in February 1987. By October 1991 only three remained in service with FreightCorp. One was repainted into CountryLink livery for use as a depot shunter at the XPT Service Centre.
Disposals commenced in 1990 with three sold to the Canberra Railway Museum. Four were sold to the Manildra Group in 1991. Many were sold to Queensland sugar cane companies for conversion to 610 mm (2 ft) gauge. A number have also been preserved.
The following are held by recognised preservation organisations:
- 7307 & 7321: Owned by the Oberon Tarana Heritage Railway, both in Patrick Portlink red and yellow livery
- 7320 & 7324: Privately owned, currently stored in Canberra
- 7329 & 7335: are both at the Dorrigo Steam Railway & Museum
- 7344: Owned by RailCorp, in custody of 3801 Limited, stored at Eveleigh Railway Workshops
- 7350: Preserved by Transport Heritage New South Wales at the Broadmeadow Locomotive Depot
The following units were sold for further commercial operation, some being converted to 610 mm (2 ft):
- 7304, 7306, 7308 & 7341: all stored in original condition at the former North Eton Mill shed and owned by the Mackay Sugar Limited
- 7305, 7328, 7330 & 7331: all rebuilt and operational at Farleigh Mill
- 7309, 7336 & 7347: all stored in original condition at Kalamia Mill, Ayr
- 7310, 7318, 7325, 7346 & 7348: all rebuilt and operational at Invicta Mill
- 7313: rebuilt and operational at Pleystowe Mill
- 7314 & 7339: both rebuilt and operational at Proserpine Mill
- 7315 & 7319: restored and operational at Shoalhaven Starches, Bomaderry, owned by the Manildra Group both ex Canberra Railway Museum
- 7317: rebuilt and operational at Plane Creek Mill
- 7327 & 7332: both stored in derelict condition at Mackay Sugar Co-op
- 7337 & 7343: both rebuilt and operational at Marian Mill
- 7340: restored and operational at Narranderra Mill, owned by the Manildra Group
- 7349: stored in original form at Pioneer Mill, Brandon
- 7322 & 7333: both stored and are now owned by the Manildra Group both ex CRT Group
- Oberg, Leon (2007). Locomotives of Australia 1854-2007. Rosenberg Publishing. p. 328. ISBN 1-877058-54-8.
- Clark, Peter J (1973). An Australian Diesel Locomotive Pocketbook. Australian Railway Historical Society NSW Division. ISBN 0-909650-02-0.
- Australian Model Railway Magazine. November–December 1978. pp. 18–25. Missing or empty
- "Locomotives" Railway Digest March 1987 page 80
- "73 Class" Railway Digest January 1992 page 22
- "Saving Diesels" Railway Digest September 1990 page 330
- "73 Class" Railway Digest November 1991 page 415
- 73 Class (Rebuilds, 610mm) Railpage
- "73 class get a new lease of life" Railway Digest May 2000 page 36
- 73 class Railpage
- 73 Class Vicsig
- Locomotive, Diesel Shunting 7301 Department of Environment & Heritage.
- Locomotive, Diesel Shunting 7344 Department of Environment & Heritage
-  Railpage
-  Vicsig
- "Touring the Classics" Railway Digest June 2010 page 24
- Locomotives Orana Tarana Heritage Railway
- New South Wales Rail System Locomotives. Sydney: Archives Section, State Rail Authority of New South Wales. 1984.