As part of the planned electrification of the entire network after the First World War, the SBB needed a universal locomotive for lines in the flat country. An engine with three driven axles, an output of 2,000 hp, a top speed of 90 km/h and a maximum axle load of 20 tonnes was specified. In addition, special scenarios were specified that had to be completed within a certain time. For example, this involved three round trips on the 117 km route between Villeneuve and Brig with a 480-tonne passenger train. These should be able to be completed in a total of 11.5 hours, including a 15-minute stop at the end stations. In response to these requirements, BBC developed the Ae 3/6I, Oerlikon the Ae 3/6II and SAAS the Ae 3/5.
Since Oerlikon did not have a tried-and-tested single-axle drive to offer at the time, Switzerland's last faster rod-driven electric locomotive was developed. It was based on the Fb 3/5 No. 11201 developed for the Gotthard Railway and, like these, had two motors that drove three axles via crankshafts, triangular connecting rods and coupling rods. The traction motors each weighed ten tonnes and, with a diameter of 1,800 mm, were the largest ever used in an SBB locomotive.
Since only one transformer was now required and this could not be arranged in the middle for reasons of space, an asymmetrical axis arrangement was used. At the end of the locomotive where the transformer was located, there was a bogie with lateral play of 80 mm. At the other end there was only a bissel axle, which had a play of at first 83 and later 70 mm. The middle drive axle could also slide by 15 mm. Despite the rod drive, this chassis was enough for the specified maximum speed of 90 km/h, which was even increased to 100 km/h in 1929.
After the first 20 vehicles, some weak points became visible, which were remedied in the next 40 vehicles. In the first series, the transformer proved to be too small compared to the traction motors, so later a stronger but lighter one was used. The steps of the tap changer in the lower portion were also distributed too roughly, which led to rough starting behavior and led to a different distribution in the later engines.
Initially, the production of the locomotives was faster as the area of application grew with progressive electrification. As a result, some locomotives were temporarily classified as surplus, although all express, passenger and freight train traffic between Basel and Lucerne was handled with the Ae 3/6II. The 60 engines were soon spread over a large area in the flatter parts of northern Switzerland, but were increasingly pushed east with the advent of the Ae 4/7. Later they were increasingly used in tasks such as the pilot service and were discarded between 1965 and 1977. Today only the number 10452 is preserved, which is used every now and then and carries the number 10439.