The U-Bahn is split in two stations: "Hauptbahnhof Süd" (south) and serving the lines U1 and U3. This part of the station had been included in the 1900 planning for the new station (the construction for the subway started in 1906, the "ring" was opened in four stages between February and June 1912. Until 28 September 1968, this station was simply called "Hauptbahnhof" without any suffix. There were two lines: the original "Ring" (opened in 1912) and the southeastern branch line (opened on 27 July 1915) leading to Rothenburgsort, the tracks and stations of which have been destroyed in the Operation Gomorra on 28 July 1943 and never been rebuilt.