Developed as the first electric locomotive of the NSB, the El 1 was intended for the line between Oslo West and Brakerøya that had been converted to standard gauge and electrified in 1920. It was built completely in Norway with the mechanical part coming from Thunes and the electrical part from Per Kure. In general arrangement, dimensions and appearance it is similar to two German locomotives: the Bavarian EG 2 (later DR E 70²) and the Prussian EG 511 to EG 537 (later DR E 71). This meant that the body was of a crocodile-like or steeplecab design and that there were two two-axle bogies which each had one traction motor that worked on a crank axle and coupling rods. 

In 1922 and 1930, a total of 22 were completed and initially used on the above-mentioned line. Over time, some locomotives also came to other lines and in 1930, two more were built. As these were somewhat heavier, they were designated El 1b and the original ones were now El 1a. They were retired between 1966 and 1973. In this process, two were sold to Rjukanbanen, of which one is now on static display at the Hamar museum. Number 2011 is also being preserved by the same museum and still operational.