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.

At the time of the First World War, the government of the Canton of Bern decided that the branch lines of the BLS Group should be electrified and operated with the abundant water power available in order to do something about the acute shortage of coal. An electric locomotive had to be developed for these railways, which would achieve a low axle load and could replace the existing steam locomotives in all train types. This meant exactly that at 1.5 percent 310 tonnes should be pulled at 35 km/h, as well as 180 tonnes at 2.5 percent at the same speed. In addition, these speeds should not only be maintained, but it should also be possible to accelerate these weights from a standing start to the specified 35 km/h within four minutes.

To speed up development, a scaled-down version of the Be 4/6 introduced at the SBB at the same time was created. 14 units were initially built in 1920 and three more in 1924, which were slightly more powerful and 10 km/h faster. They were spread among the BLS subsidiaries and, if necessary, exchanged with one another. Since they were created by order of the government, they quickly earned the nickname “decree mills”.

In their original design, the locomotives had two bogies, each with two coupled axles and one carrying axle. The buffers and couplings, as well as small hoods were attached to the bogies. This meant that the locomotives could actually be assigned to the design of the crocodiles, which, however, was rarely actually stated due to the very small front end. The power came from a traction motor that stood on the bogies and drove a jackshaft.

Schematic drawing with dimensions

Locomotive Magazine, May 1921

Between 1954 and 1956, the carrying axles and front hoods were removed from the ten most recently built locomotives, since the branch lines could now cope with the higher axle loads. They could now come up with a higher adhesion mass and were given the designation Ce 4/4. The engines that were not converted were retired by 1973 at the latest, the converted ones between 1975 and 1988. Two units with only one traction motor were in service for a long time as shunting locomotives in the Böningen workshop. A Ce 4/6 and a Ce 4/4 are still preserved today.

The F 2x3/3 was the counterpart to the Fb 2x2/3 in the trial runs for the Lötschberg railway. It was ordered from the Swiss locomotive and machine factory in Winterthur and got the electrical equipment from Oerlikon. Unlike its competitor, it was a single-frame locomotive standing on two bogies. These each had three coupled axles and no carrying axles and were coupled to one another. The series motors acted on the inner axles via jackshafts and diagonal rods. Because the axles were fixed in the inner frame, the running characteristics had to be compromised. Since the couplers and buffers were also located on the bogies, the locomotive frame was relieved of the pulling and pushing forces.

Since the housings of the engines were open, it was found that the targeted hourly output of 1,000 hp could be maintained without the ventilation switched on and that this could also be used effectively as a continuous output. The locomotive thus reached 42 km/h at a gradient of 1.55 percent with a car load of 500 tonnes. At 2.7 percent, it was still able to maintain the same speed with 310 tonnes and was therefore superior to the Fb 2x2/3. The fact that the top speed later had to be reduced from 70 to 60 km/h due to the chassis design was accepted. The locomotive continued to be used and was renamed Ce 6/6 according to a new scheme, but was increasingly used on flatter routes with the appearance of the more powerful Be 5/7. In 1928 it was sold to the Bern-Neuchâtel Railway and remained in service there for another 40 years. It was then scrapped, but one bogie with attached traction motor has been preserved and can be viewed in the Lucerne Museum of Transport.

Shortly after its founding in 1906, the Bern-Lötschberg-Simplon Railway decided to electrify the Spiez-Frutigen Railway it operated and to do the same on the Lötschberg Railway that was yet to be built. Single-phase alternating current with 15,000 volts and 15 Hertz was chosen as the power system. In the search for a suitable electric locomotive, two examples were ordered for comparison: the Fb 2x2/3 shown here from Krauss and AEG in Germany and the F 2x3/3 from SLM and Oerlikon in Switzerland. The Fb 2x2/3 was a two-section locomotive consisting of two identical and technically independent halves.

Each section sat on two coupled axles and one carrying axle. For better negotiation of curves, the respective outer coupled axle was laterally movable and the carryling axle was radially adjustable and these two were connected to form a Krauss-Helmholtz bogie. The sections were connected by close coupling and pre-tensioned with buffers. With this chassis, the locomotive was superior to its competitor in terms of driving characteristics. The transformers were in the low hoods on the ends, while each section housed a large, low-speed repulsion engine in the engine rooms. The power was transmitted without a gearbox to a crankshaft and finally via the coupling rods to two axles each. With 800 hp per motor, the locomotive could pull 400 tonnes at 40 km/h at 1.55 percent, and 250 tonnes at 2.7 percent. After the most important railway administrations in the German Reich had agreed on operation at 15,000 volts, but 16⅔ Hertz, the line and the locomotive were also switched to the other frequency.

Although the locomotive met the requirements in terms of driving characteristics, traction and control systems, there were repeated problems with overheated bearings in various places. It was also a problem that more than 100 percent of the nominal power was required to start the locomotive. It was thus returned to AEG, where it was transferred to the Prussian State Railway as the EG 509/510 for testing purposes. Since there were plans to electrify the Berlin suburban lines, the locomotive was first used on the Dessau-Bitterfeld line and was fitted with pantographs. Since both sections were independent, journeys were made with one section each in front of and behind the train or with just one section. With the cessation of electrical operations on the line during World War I, the locomotive was shut down and officially retired in 1923.

After the tests with the two electric locomotives on the Spiez-Frutigen route, conclusions were drawn from the experience as to what a new, series-built locomotive should look like. The F 2x3/3 impressed with its power train, while the Fb 2x2/3 with its carrying axles improved running smoothness and the ability to negotiate curves. That is why the decision was made to order a similar power train from the manufacturers of the F 2x3/3 locomotives, but instead of bogies they were equipped with coupled axles fixed in the frame and a carrying axle at each end. Additional electrical assemblies were supplied by BBC to shorten delivery times. A total of 13 locomotives were delivered in 1913, which were to pull both freight and passenger trains on the newly built mountain route, including the 14.6 km long Lötschberg tunnel.

In order to achieve good running characteristics, three of the five driven axles could be moved sideways. While the middle one could be moved by 25 mm, the first and fifth were each mounted with the adjacent carrying axle in a Krauss-Helmholtz bogie. With the lateral deflection of the carrying axles by a maximum of 78 mm, they were moved by up to 40 mm. Despite the five driven axles, this made a fixed wheelbase of just 4,500 mm possible.

Between the second and third, as well as between the third and fourth coupled axles, there was a 14-tonne series motor on the frame, which drove a jackshaft via a Citroën gearbox underneath. By means of a rod triangle on each side, both engines acted on the middle axle. Since the rod triangles often broke under the high load during operation, they were later replaced with cast pieces. In order to achieve a large number of speed steps with a relatively small number of taps on the transformers, the next of the twelve steps of only one of the motors was switched alternately to obtain a total of 24 steps.

Schematic drawing

Die Lokomotive, June 1914

With an hourly output of 2,500 hp, the Fb 5/7, which was soon renamed the Be 5/7, was the most powerful electric locomotive in the world. On the ramp with a gradient of 2.7 percent, it was able to pull trains weighing 330 tonnes at 50 km/h. After the predecessor locomotive had been moved to flatter routes, the Be 5/7 was the only locomotive used on this route. Thanks to the good running characteristics, the locomotives were later approved for 80 instead of 75 km/h, one locomotive was even equipped with four smaller motors and could run 90 km/h. From the second half of the 1940s, they were increasingly pushed into freight train service b the Ae 4/4 and when the Re 4/4 were delivered in 1964, they were quickly scrapped.