When the Blackwater and Goonyela lines were electrified in the eighties, QR ordered 86 powerful electric locomotives from Comeng for coal traffic. Each locomotive had two cabs and three two-axle bogies. The electric part came from Hitachi, with the support of General Electric. To put some locomotives into the middle of the train, they were equipped with a radio control system, what led to the class 3100 being set up to be used as lead locomotives and the class 3200 being set up to be used as slaves.
With a total of five locomotives, trains contained up to 120 cars with 106 tonnes each, leading to a total weight of 12,720 tonnes plus the weight of the locomotives. Starting in 2003, 63 locomotives were rebuilt to the class 3700 by Siemens. One cab was removed and they received three-phase AC traction motors and a new distributed power system, eliminating the need for separate lead and slave locomotives. Now only three locomotives were needed for the heaviest trains since the tractive effort had grown with the new traction motors. From 2007, more locomotives were built new with the same equipment, which were designated class 3800.
