The 3500/3600 class locos were introduced into service in 1986 for use in the southern coal fields (Blackwater System). They were built by Clyde Engineering and Walkers Ltd. The electrical systems were supplied by ASEA Brown (now Adtranz/Bombardier).

All members of the 3500 & 3600 class are based at Callemondah on the outskirts of Gladstone. The 3500 class are fitted out as command locos (air-conditioning, locotrol, toilets, stove etc.) while the 3600s are used as slave/remote locos.

The 3500 and 3600 class locos occasionally make trips to Brisbane for attention on the wheel lathe at Mayne. They are treated as an out of gauge movement due to the ladders on the sides.