During the war years in the early 1940s, the South Australian Railways (SAR) had a desperate need for additional tractive power on increasingly growing troop and supply trains and with the combined need for quick acceleration and high speed running on the flat and general straight mainlines to the north to Port Pirie, as well as power "under the belt" for the long 19 miles , 1-in-45 (2.2%) graded slog up the Adelaide Hills to Melbourne, a new locomotive design was required by the SAR.