NSB ordered three El 9 locomotives from Thune on 4 October 1940. The units were delivered in 1942, with the electrical components from NEBB and the transformers and controllers from Per Kure. A delay was caused by bombing of Per Kure by the resistance. The locomotives were custom-built for the steep gradients on the Flåm and Hardanger Lines, and were delivered with an axle load of and a Bo'Bo' wheel configuration. The locomotives weighed and the maximum permitted train weight was . If the trains were to stop at Kårdal, the weight was further limited to .