During the 1980s, NSB started leasing SJ T44-locomotives from Sweden to supplement the Di 3. In 1992, the decision was made to order 12 Di 6 and 20 Di 8 to replace the Di 3. The former was based on the Di 4 and had twice the power of the Di 3. The Di 8 was slightly more powerful than the Di 3, and were intended for freight trains. Both series were put into service in 1996, but the Di 6 proved to have so many technical problems that they were returned to Siemens in 1998. The Di 3 units had been set aside and some had been scrapped, but the return of the Di 6 forced NSB to put the units back into service.