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.