Swiss Federal Railways Re 4/4^II

The Re 4/4^II is a four-axle multipurpose locomotive designed in the sixties by a collaboration between SLM, BBC, MFO and SAAS. Requirements were more power than the Re 4/4^I and the approval for train type R that allows higher speeds in curves. A challenge was that the train type R had only been used on light locomotives with an axle load of 16 tonnes or less by this time. Fortunately, test runs had proved that this was no problem with this locomotive and an approved top speed of 140 km/h was feasible.

This was partly possible thanks to a flexible joint between the bogies that guided the rear bogie when the front one entered a curve. On the outside, the design resembled the Ae 6/6 and the later Re 6/6. But with an hourly output of 4,700 kW or 6,300 hp, it was more powerful than the six-axle Ae 6/6. Power and dynamic braking was controlled with an up-down-lever that automatically checked the current and thus enabled to utilize full power without risking overload. The dynamic brake was able to feed power back into the overhead line.

The six prototypes were delivered in 1964 and by 1985, a total of 273 made the Re 4/4^II the largest class of locomotives in Switzerland. They could often be seen in multiple with a Re 6/6, this combination was in fact so ubiquitous that it was called Re 10/10. The 26 locomotives of the type Re 4/4^III were based on the Re 4/4^II, but had a slower gear ratio.

Later they became the Re 420. The Re 421 was created from 1999 when 21 Re 420 were rebuilt for use in Germany, for which they received PZB and LZB and a modified pantograph. They came to SBB Cargo, but were sometimes loaned to the passenger branch. From 2002, a large number of locomotives got air conditioning for the cabs. Between 2011 and 2016, 30 underwent the LION modernization program for use on the Zurich S-Bahn. They received a more modern variant of multiple controls and are being used in sandwich mode with double-decker coaches. By now, a larger number of former Re 4/4^II has been withdrawn.