nearly identical to Oe and was a twin unit locomotive with a combined power output of . Four twin units were delivered in 1925, and a fifth in 1929. The El 4 locomotives were longer and more powerful, and operated as singles. Each single El 4 had the same power output as a twin El 3. Two units were delivered in 1926, two in 1928 and one in 1929. NSB operated the trains using their rolling stock from Narvik to Abisko, where there was a change of locomotive and operating company. In 1940, the Port of Narvik suffered extensive war damage, and all export for the remainder of World War II went via Luleå. In 1957, the Government of Sweden bought LKAB. Two of the El 4s were damaged beyond repair during the war. In 1949, pooling of the locomotives started, whereby NSB and SJ would alternate operating trains and their respective locomotives used on the whole section from Kiruna to Narvik. The following year, LKAB decided to increase annual transport from 8–10, to 12–15 million tonnes. This involved increasing the train weight to . To provide sufficient hauling power, the El 3 units were rebuilt from twins to triplets, and two of the El 4 units were made a twin unit. The upgrades were completed by 1953. At the same time, SJ decided to order a new type of locomotive, the Dm. NSB followed suit, and took order of six locomotives, each with a power output of . They were designated El 12 and were delivered in 1954, with another two delivered three years later. The locomotives were at first used as four twin units, but later six were rebuilt to make two triplets. During the 1960s, LKAB again decided to increase the need for transport, and NSB ordered six El 15, with a power output of . Although never permanently coupled together, the units normally operated in pairs when hauling ore trains. The El 4 was used until 1964, and El 3 until 1967. Neither the El 3, El 4 or Oe has been preserved. 1980–1997 In the 1980s, LKAB started to push for lower transport costs. At the time, NSB had a 50% profit margin on the operations, or about NOK 60 to 70 million per year. A committee was established by both countries' transport ministries to find areas of improvement. During the 1970s and 1980s, the