The Re 620, Re 6/6 in the old numbering scheme, are six-axle, electric locomotives of the SBB-CFF-FFS, which were acquired as a replacement for the Ae 6/6 for heavy services on the Gotthardbahn. They are the most modern of the so-called "Gotthard locomotives". Construction and Technology To reach the necessary tractive effort, a construction comprising six driven axles was necessary. In order to still get good running characteristics in curves, they were built into three two-axle bogies instead of two three-axle bogies as on the Ae 6/6. The middle bogie can move sideways, and the three bogies are connected by elastic cross couplings. Two of the four prototypes were built with a split locomotive body, whereby the joint may only move on an horizontal transverse axis to allow for changes in gradient, similarly to the Rhaetian Railway Ge 6/6 II. The other two prototypes got a softer secondary suspension instead of the joint, which proved to be so reliable in everyday use that all series locomotives were built this way. Nevertheless, the two prototypes with a split body are still in regular operation. The exterior design is similar to the Re 4/4II, as are the driver's controls and the conventional transformer technology with fixed running notches, which was applied for the last time for this locomotive. In contrast to the Re 4/4II, the Re 6/6 has two transformers (one power and one control transformer), which are mounted on the frame between the bogies. Due to the higher roof, the Re 6/6 looks more brawny than the Re 4/4II, especially when seen from the front side. Operations The Re 6/6 is equipped with multiple unit train control together with Re 4/4II, Re 4/4III, Re 4/4IV and RBe 540. In passenger traffic they pull heavy passenger trains over the Gotthard route (as an alternative to a double heading of Re 4/4). In freight traffic they are used all over Switzerland for heavy trains, on the Gotthard route very often together with an Re 4/4II or Re 4/4III. Such a couple, often referred to as "Re 10/10" (both locomotives are Re class, so the couple is Re class; 10/10 means that they overall have 10 driven axles out of 10), is capable of pulling the maximum train weight of on 2.6% gradients of the Gotthard line. For heavier trains, up to 1600 tons are operationally feasible; an additional bank engine has to help