The Re 6/6 are six-axle electric locomotives of the Swiss Federal Railways, acquired as a replacement for the Ae 6/6 for heavy service on the Gotthard line. With a power output of 7,850 kW and a top speed of 140 km/h, the Re 6/6, which was first put into service in 1972, remains one of the strongest locomotives in Switzerland to this day. Later referred to as Re 620, they were equipped with a driver's cab air conditioning system starting in 2005.