As the Ae 8/14 double locomotives were too huge for express trains on the Gotthard, the SBB ordered a new type of locomotive in World War II that was essentially half an Ae 8/14 with two cabs. It had to have multiple controls to use two locomotives together when required for a heavy freight train.

The locomotives had four powered axles in the main frame and one leading axle on each end. The central carrying axle of the Ae 8/14 could be dispensed with due to weight reductions in some places. Each leading axle and the adjacent driving axle formed a Java bogie, with lateral play of 120 and 20 mm, respectively. Power was transmitted via the SLM universal drive. The dynamic brake was able to feed power back into the overhead line. With an hourly output of 4,200 kW, they were able to haul 375 tonnes at 2.6 percent with 75 km/h. The top speed was 125 km/h.

Between 1941 and 1944, twelve were built by SLM with the electrical part from BBC, Oerlikon and SAAS. The NS received ten locomotives of class 1000 in 1946 which were basically a variant of the Ae 4/6 for the Dutch DC network. Now the Ae 4/6 was the standard express locomotive on the Gotthard. They were rarely used in freight traffic since they tended to slip with heavy loads and the multiple controls often made problems.

Between 1961 and 1966, seven were rebuilt with the BBC spring drive. At the same time, the Ae 6/6 became the new standard express locomotive on the Gotthard. Now the Ae 4/6 was assigned to other tasks like helper service. The last one was withdrawn in May 1983 and all were scrapped.