The Be 4/6 No. 12303 to 12342 were 40 electric express locomotives ordered by the SBB for service on the Gotthard. They were directly based on the Fb 2x2/3 prototype No. 11302 and had already been ordered in 1918 when the prototype had not yet been completed. The requirements included a top speed of 75 km/h and the haulage of 300 tonne trains on the Gotthard ramps with 50 km/h.
The mechanic part was produced by the SLM, while the electric part came from BBC. The locomotives had two bogies with two driving axles and a leading axle each. Each bogie had two traction motors which acted on a common crank axle and powered the driving axles via coupling rods. The first batch of twelve built in 1919 had 1,230 kW and did not have a dynamic brake. Three other batches built in 1920 and 1922 delivered 1,500 kW and had a dynamic brake. The first 27 locomotives could be switched from 15,000 to 7,500 V since the Gotthard line had been operated with the lower voltage while steam locomotives were still in use.
Although they met all requirements and surpassed some of them by a wide margin, they were not popular among the crews due to vertical oscillations. As early as in 1929, all expresses on the Gotthard were taken over by the Ae 4/7. Now, the Be 4/6 was used for regular passenger and freight trains and as helpers on steep grades. Over time, they only got small modifications to meet operational requirements. They were withdrawn between 1965 and 1976.
