A total of six 700 class locomotives were built for the South Australian Railways by AE Goodwin, Auburn and are an Alco DL500g model. They were built in 1971/72, with the first three delivered on broad gauge bogies and the last three on standard gauge bogies. In March 1978 all were included in the transfer of the South Australian Railways to Australian National. Over the years the locomotives frequently switched gauges before all were put on the broad gauge in 1987. Following the Adelaide-Melbourne railway line being converted to standard gauge in 1995, all of the 700 class were transferred to standard gauge. The 700 class operated on all main lines in South Australia as well as interstate to Broken Hill and Melbourne.
In 1986, a new computer system required the class leaders of the former South Australian Railways to be renumbered as the last member of the class, with 700 becoming 706. In June 1994 702 was damaged by fire and a New South Wales 442 class locomotive was purchased with the intention of combining the two locomotives as one but the plan did not proceed and both were scrapped.
The remaining five were included in the sale of Australian National to Australian Southern Railroad in November 1997. As of January 2016 all locomotives are now stored with 701 (since December 2015), 703 (since December 2015) & 704 (since 2014) stored serviceable and 705 stored after a major failure in 2015. 706 had been in long term storage after a major failure in 2005 and has been scrapped during 2016