For the ore mining areas in Kiruna and Gällivare in northern Sweden, the ore railway between the Swedish port of Luleå and the Norwegian port of Narvik had already been electrified in the 1920s. When the mining quotas rose sharply after the Second World War, significantly more powerful electric locomotives than those already in existence had to be developed. From 1953, the Dm was created, which consisted of two permanently coupled locomotives with a 1-D wheel arrangement and which had evolved from the Da. With these locomotives, 3,400 tonne ore trains were to be transported from the mining areas either to the port of Luleå on the Gulf of Bothnia or to the Norwegian port of Narvik, which was ice-free all year round.

In each half of the locomotive there were two motors, each with 920 kW, which acted on a jackshaft in the middle between the four coupled axles. The further power distribution then took place via connecting rods. The Norwegian State Railways, which also had a share in the ore railway, ordered four pairs of locomotives of this type and designated them as El 12. The special feature of these was that they could be operated separately and individually during daily service. Starting in 1962, the motors were replaced with new ones with 1,035 kW, and the engines newly built from that point on received 1,200 kW each, so that each double locomotive had an output of 4,140 or 4,800 kW. By 1971, a total of 76 locomotive halves were built, from which 38 double locomotives could be formed.

In order to do justice to the ever increasing mining quotas, middle sections were built without a driver's cab and carrying axle and these were coupled between two type Dm locomotives. Ultimately, all locomotive halves with the 1,200 kW motors were used to build three-section locomotives. Since the middle part was called Dm3, the combination Dm+Dm3+Dm was soon also simply called Dm3.

Although the two-piece locomotives were also very powerful, the Dm3 were considered the longest and most powerful electric locomotives of their time. Initially, all locomotives were used on the ore railway, but after increasing train weights, the two-part locomotives were moved to more southern areas around 1980 and were used for regular freight trains for a few more years. In the 1990s, the Dm3s underwent a major overhaul, with new electronics installed and driver comfort significantly improved. The modernized locomotives could now be recognized by their blue-grey-red paintwork instead of the previous brown paintwork.

In 1996 all existing ore railway locomotives were handed over to the private MTAB Malmtrafik i Kiruna AB. The two two-part trains were renumbered to Dm2 and scrapped the following year, but the three-part trains were used longer. From the year 2000, the MTAB procured the modern IORE locomotives from Siemens, which gradually made the Dm3 superfluous. The last ones were still in use when in 2012 the MTAB was renamed LKAB Malmtrafik AB after the operating company of the mines, but this changed in 2013 after all IORE had been delivered.