The first diesel locomotive used by NSB was a single Di 1 unit delivered in 1942. It was more cost-efficient than the steam locomotives used on the non-electrified lines, and in 1945, NSB decided that it would not order more steam locomotives. General Motors' Electro Motive Division (EMD) made a bid to deliver twelve units based on their F7, and NSB agreed to lease a single unit for trial. The body and mechanical components were built by NOHAB, the motors by ASEA and prime mover by EMD. While under production in 1954, GM shipped a G12 for trial in Norway and Sweden. It was tested on the express train on the Dovre Line on 7 August, but proved to have insufficient power, causing the train to be 20 minutes late.