In 1969 the SAR began to receive a large number of four-axle electric locomotives which had considerably more power than the 5E. They were constructed by the Union Carriage & Wagon Works and their electric part was supplied by AEI and English Electric. The first orders were for 82 6E locomotives and 20 6E1 which had re-designed bogies. Since the 6E1 design was found to be superior, ten more batches of this design were built, resulting in a total number of 960 locomotives of the 6E1.

In 1990 and 1991, some were coupled semi-permanently in pairs and reclassified 16E. Also in the nineties, some were rebuilt to 17E with improved regenerative braking and wheelslip control systems. A larger rebuild of most 6E1 locomotives started in 2000 when they were converted to class 18E where one cab was stripped from all its controls. These will remain in service for some time, while most 6E locomotives were withdrawn by 2015.