A total of 50 of these B-B type were built by Walkers of Maryborough in Queensland for the NSW railways over 1970-1973. The prime mover was a Caterpillar D379 series B four stroke V8 diesel with a gross output of 700 hp (522 kW). The total loco weight was 50 tonnes.
"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."