The O series was built for theMalmbanan (Iron Ore Line), the firstelectrified mainline railway in Sweden.[i] ASEA started testing out technology with a test unit in 1908, and by 1914 the first Oa locomotive was delivered, along with the passenger haulingPa. At first it was the northern part of Malmbanan, fromKiruna toNarvik that was electrified. Thesteam locomotives had been hauling 28 wagons at 10 km/h, but the new agreement signed in 1913 withLKAB meant that SJ had to haul 40 wagons at 30 km/h to transport enough ore. The solution lay in a joint production betweenSiemens of Germany and ASEA. The Siemens locomotives were designatedOa while the ASEA locomotives were designatedOb. The trains had 1200kW motors.[1]
These stayed in service on the northern section until 1923 when the southern section toLuleå also was electrified, at which time they were moved to the southern section. A new series ofOe andOf locomotives were delivered. In the 1950s when larger trains were put into service, some of the Ofs were rebuilt to triple units, designatedOf3. They were also supplemented with the newDm-series that eventually replaced them.
