U55 was an U-Bahn line in the German capital city of Berlin. It connected the new Berlin Hauptbahnhof, or main railway station, to an interchange with the S-Bahn at Brandenburger Tor. It had only three stations, did not connect to any other U-Bahn line, and was operated as a shuttle line using a single train. The line was constructed as part of an extension of the U5 that was subsequently postponed due to financial difficulties. As much of the work on this disconnected section of the extension had been completed, it was decided to complete the section and open it as a separate line in 2009. In 2010, construction began on the intervening section connecting Brandenburger Tor to Alexanderplatz; on 4 June 2018, U55 was closed until December 2018 to accommodate the work needed to connect it to this new phase of the project. The complete project, merging U55 and U5 into a single line, opened on 4 December 2020. Operation of the U55 ceased on 17 March 2020 in preparation for the line's incorporation into the U5 extension. History Origins The unusual nature of U55 reflected Berlin's troubled finances. When the German government decided to move from Bonn to Berlin under the Chancellor of Germany Helmut Kohl, who also announced the reunification of Germany on 3 October 1990, it was decided to refurbish the area around the Bundestag into a modern government complex. As part of this effort, there were plans to extend the U5 from its western terminus at Alexanderplatz through the city centre, past the Brandenburg Gate and the Bundestag, to the new central train station, Berlin Hauptbahnhof. This Kanzlerlinie (Chancellor Line), so nicknamed because it passed through the government quarter, was originally planned since the 200km plan as a diagonal line through central Berlin, continuing to Turmstraße in Moabit, where it would link with the U9, and on to Jungfernheide, where it would connect with the S-Bahn ring and U7. The line was also planned to go via Tegel Airport (to be replaced by Urban Tech Republic), Scharnweberstraße towards Rathaus Reinckendorf. As this was a long-planned route, short tunnels exist at both Jungfernheide and Turmstraße to accommodate the new line. Plans were discarded as a tram was also planned to be extended west. For now, the line is only approved to terminate at the Hauptbahnhof, with the route to Jungfernheide and beyond to be built later.