For the increasingly heavier trains on the Lötschberg line, the BLS needed a new locomotive in the mid-1920s that was supposed to be more powerful than the Be 5/7. On the route with a gradient of 2.7 percent, it had primarily to transport freight trains of 510 tonnes and, if necessary, also be used in front of the heaviest express trains. Since the route was single-track and therefore rapid operation had to be guaranteed, the speed to be reached was set at 75 km/h.

Since a rod drive fell out at the required speed, it was not possible to fall back on a type that had already been developed, such as the SBB Ce 6/8 II. The choice fell on the Secheron spring drive with double motors, a form of the quill drive. The locomotive stood on two bogies, each with one leading and three driving axles, which were coupled to each other. For the first time in Swiss history, there was a seat in the cabs so that the driver no longer had to stand.

With a maximum speed of 75 km/h, the locomotive was assigned to train series B, which led to the designation Be 6/8. In the years 1926 to 1931 only four pieces were made at Breda, another four were made between 1939 and 1943 at SLM. The second series was approved for 90 km/h with a different gear ratio and the locomotives of the first series were soon rebuilt in the same way. This was accompanied by a classification in the train speed row A, which led to the designation Ae 6/8, which is better known today.

The train weight of the freight trains over the Lötschberg was increased in the first few years with the Be 6/8 from 510 to 550 and finally 600 tonnes. As planned, they also took over express trains that were too heavy for the Be 5/7. They were the most powerful locomotives in the world until the SBB introduced the Ae 8/14 two-section locomotive in 1931. From 1960, thanks to engine to the chassis, the speed could be increased to 100 km/h. The last machine was only retired in 1995 and today there are still three preserved.