With 277 locomotives, it is the largest locomotive series in Switzerland. The Re 4/4 II was built from 1964 to 1985 and is still in operation today. With the commissioning of the Ae 6/6 at the Gotthard, a fast and powerful locomotive for express trains became available. However, the tracks were heavily stressed due to the two three-axle bogies, which particularly limited the curve speed of the Ae 6/6. The Re 4/4 II provided a locomotive that could also travel quickly through curves. The locomotive delivered 4700 kW, reached a maximum speed of 140 km/h, and was therefore classified as a Class R locomotive. The design was based on that of the Re 6/6. Both locomotives occasionally operate as Re 10/10 in double traction. Due to a lack of alternatives, some locomotives were specifically modified for the Swiss Express. They received an extended buffer beam, new couplings, and a paint scheme in the Swiss Express colors of orange-gray-orange. Additionally, they feature the SBB logo instead of the Swiss cross. Other Re 4/4 II locomotives were later further modernized, receiving features such as single-arm pantographs, rectangular halogen headlights, and driver’s cab air conditioning. Besides the SBB, the locomotives are also in service with the BLS and other Swiss railways.