On the two narrow-gauge lines that comprised the truncated north–south routes along which huge amounts of materiel and troops had been carried during the war, some of the locomotives had 50 or more years of use.

Their condition had been worsened in the harsh outback environment through constant jolting – the track was lightweight and much of it had been laid on bare earth 60 years earlier.

After post-war economic restrictions had moderated, in 1950 the federal government provided funding for the Commonwealth Railways to replenish its fleet of both narrow and standard gauge locomotives and rolling stock.

[1] A call for tenders issued for 14 diesel locomotives for the Commonwealth Railways narrow-gauge lines included some important criteria: Thirteen companies submitted more than 30 designs.

The engine in the winning tender, by the Birmingham Railway Carriage and Wagon Company Ltd, was a Sulzer plant with a maximum speed of 750 rpm.

[note 3] Any doubt was resolved by the purchase contract stipulating that Sulzer Bros (London) Ltd would accept full responsibility for the design and performance of the completed locomotives.

Still temporarily mounted on standard-gauge bogies on which it had been trialled in the UK, NSU51 was unveiled at Port Augusta on 12 June 1954 with nameplates showing George McLeay (whose portfolio included the Commonwealth Railways) on the cab sides.

[9][10] On 26 June 1954, locomotives 51 and 52 worked the first diesel-hauled northbound Ghan into Alice Springs – timed to coincide with a visit of Prime Minister Robert Menzies.

[12][13] It was initially expected that the new locomotives would be able to complete a 1370 kilometre round trip from Oodnadatta to Alice Springs on one tank of fuel.

[14] Minor faults with voltage regulators and air and oil filtration systems were quickly rectified, and the design went on to earn a reputation as an efficient and robust unit.

Crews reported, for example, that the spring-loaded, 18-notch throttle handle stayed in the selected position when new, but as it wore, it would swing unpredictably and cause the train to lurch violently.

The NSU fleet remained intact until the Central Australia Railway was superseded by the opening of a new standard-gauge line to Alice Springs in 1980.

To Roberts Construction for removal of narrow gauge infrastructure from northern part of Central Australia Railway June 1981.

To Roberts Construction for removal of narrow gauge infrastructure from northern part of Central Australia Railway June 1981.