After the electrification of the federal German network reached Cologne from the south in the late 1950s, the Cologne–Aachen route was also electrified. This involved the conversion of several tunnels into cuttings. Due to the different power system of the Belgian State Railways, Aachen Hauptbahnhof was upgraded to become a system change station, the first (and for 42 years the only place) where the German and Belgian rail electrification systems met directly. With the change of timetable in May 1966, electric train operations commenced on the Cologne–Aachen–Liège route, using the standard Belgium system (3000 V DC) from Aachen. (Liège had been accessible for electric operations from Brussels since 1955.) At that time, Belgium already had a multi-system locomotive. In the autumn of 1966, DB also received its first multi-system locomotives, which could run under both the German and Belgian electric systems, but did not prove themselves, so that ultimately only some of the international express trains were hauled with Belgian multi-system locomotives and the others still had to change locomotive in Aachen until the 1990s.