The DL class provided the first diesel locomotive in service in Queensland, DL 1 being built to provide a light weight (maximum 6-long-ton or 6.1-tonne or 6.7-short-ton axle load) locomotive for the Mt Surprise - Forsayth section of the line from Mareeba, which since cyclonic rainfall in 1927 severely damaged the line, had only been able to support a rail motor hauling 1 or 2 goods wagons. DL1 was built by Queensland Railways in 1939, initially with C wheel arrangement but after rough riding during trials around Brisbane it was returned to the workshops and fitted with a pony wheel.
DL2 was built by Robert Stephenson and Hawthorns in 1954 and the final two were built by Walkers Limited in 1961. They were initially used exclusively west of Mt Surprise on the lightly trafficied line to Forsayth. When traffic on that line grew to the point where upgrading it to 10-long-ton or 10.2-tonne or 11.2-short-ton axle load was justified, the DL class was replaced by the 1720 class, and the 4 locos were then used as shunters at various locations.