Though SJs first electric locomotive was the Oa series used on Malmbanan, it was not suitable for use on the main lines, due to low speeds.

To solve this problem SJ surveyed a large section of locomotives abroad, before concluding with a design and placed an order with ASEA for 50 units.

The first units were delivered in 1925 and tested on Malmbanan until Västra Stambanan between Stockholm and Göteborg was finished in 1926.

Through the history of production the original wooden body was replaced with a steel construction.

Production halted after a more powerful engine was introduced and new locomotives were designated Dk.

Dg was the other original D-locomotive, geared for maximum 70 km/h and optimized for freight trains.

This is the last series of locomotives that was built new, all later types have been rebuilt, except the one-off experimental subtype Dr.

When the production of Da-locos started in 1953, the Dks were rebuilt to the same engine, and received the designation Du.

This locomotive came into existence during the 1950s when the Dk, Ds and Dg locos were upgraded to motors of the same type as in Da.

It disappeared from service in 1977, with the dismantle of the wooden locos, while the steel units were rebuilt to Du2.