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.