In the first half of the Sixties, the Swedish State Railways (SJ – Statens Järnvägar) worked intensively on replacing their old side rod electric locomotives. The Swedish locomotive builder ASEA built on this goal and came up with six four-axle test locomotives in 1962 with the usual stepped relay control. Three years later a tentative conversion of road number Rb1 1001 to control with thyristor rectifiers was successful. The new technology allowed exact and variable control of the motor current without changing between various running modes. In addition, this led to a 25% to 30% higher utilization of tractive effort. Additional advantages were less risk of slippage and lower maintenance. This locomotive served as the prototype for the new class Rc, which was then bought from ASEA in six production runs of 360 units and delivered in the following 20 years. The locomotives were equipped with 900 kilowatt type motors, and they were mostly built for a maximum speed of 135 km/h / 84 mph. The ten locomotives from the Rc3 production run and the last 40 units of the class Rc6 came from the builder equipped to run at 160 km/h / 100 mph. During the long production period, various improvements flowed into this series, and there were different conversions and modifications. Changing the gearing allowed 23 units of the Rc2 and all 60 units of the Rc5 locomotives to run at 160 km/h / 100 mph (they were reclassed as the Rc3 and Rc6). With the division of the SJ into various business areas on January 1, 2001, the freight service sector Green Cargo (GC) received the Rc1, Rc2, and Rc4 units. Most of the Rc1 units are in storage and are no longer on the Green Cargo roster, while most of the Rc2 units (since converted to Rd2) and Rc4 units are still to be found pulling GC freight trains. The SJ AB (passenger train service) was given all Rc3 and Rc6 units. The former were all sold in 2014, and the latter are still used currently chiefly in passenger train service.