73 Class

The New South Wales 73 class are a diesel-hydraulic locomotive originally purchased and operated by the New South Wales Government Railways (NSWGR) of Australia, and now operated by a variety of private operators. The NSWGR were in the need of powerful diesel shunting locomotives in the 1960s. They had experimented with the 7101 and 7201. Following an order by Queensland Railways for similar units, the NSWGR placed an order with Walkers Limited for 20 B-B units fitted with a Caterpillar 485 kW diesel engine. These were the first NSWGR locomotives to be built in Queensland. Seven similar locomotives of 710Hp with the Caterpillar D398B V12 engine were purchased by the Emu Bay Railway in 1970.

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. The big floods of 1976 gave 7323 an opportunity to show off its swimming ability. In March that year, 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.