The class was the dominant locomotive on NSB's unelectrified lines. It was ordered as part of the company's dieselization of services during the 1950s and 1960s, and was initially used on the three mainline routes of the Bergen, Dovre and Nordland Lines. In the 1960s the Bergen and Dovre Lines were electrified and the Di 3 units transferred to smaller lines, such as the Meråker, Valdres, Røros, Solør and Rauma Lines. They remained in service with NSB until 2001, five years later than planned due to NSB returning their successor, the Di 6. The units are still in use by the private operator Ofotbanen, the Kosovo Railways, an operator in Sicily, and the Norwegian Railway Museum. The class is similar to the DSB Class MY, NMBS Class 52–54, CFL Class 1600 and MÁV M61.