In the tunnel, it passes the foundations of the Kaiser Wilhelm Memorial Church on a tight arc and then follows Tauentzienstraße to Wittenbergplatz where the line emerges to an elevated section via a ramp east of the Kleiststraße/Courbierestraße intersection.

From there the line runs beyond the former city limits and the elevated railway descends again into a tunnel to Vinetastraße before reaching the terminus at Pankow.

According to the model of public transport networks, which were used in various cities (Frankfurt, Shanghai, Munich, Beijing, Guangzhou) they were then designated as U1 to U9 and similarly the acquired S-Bahn routes were preceded by "S".

With the merging of Berlin in the context of German reunification and the reconstruction of the disused Wittenbergplatz–Mohrenstraße section in 1993, the BVG decided to swap the western branches of lines U1 and U2, which meet at Wittenbergplatz.

Finally, after many years and negotiations, Siemens proposal for an elevated railway line from Warschauer Brücke via Hallesches Tor to Bülowstraße was approved.

The construction work had to be carried out quickly because the contract with the city of Berlin, signed with the granting of the concession, specified that the line had to be finished within two years, or a penalty of 50,000 marks would be payable.

After tough negotiations with the city of Charlottenburg it was decided to extend the line to Knie along the Tauentzienstraße, but instead of being elevated it would be a subsurface (cut-and-cover) railway.

This allowed many prominent Berliners to participate in the opening trip, including the Prussian minister for public works, Karl von Thielen.

Under the working title of Krumme Straße, the line was initially planned with a station at Bismarckstraße (now Deutsche Oper) and a terminus at Wilhelmplatz.

[5] After the so-called "stem line" had been extended to Wilhelmplatz (now Richard-Wagner-Platz) in Charlottenburg, the elevated railway company planned to connect the Berlin city centre to the new U-Bahn.

Since there were plans at the time to build a branch line under Frankfurter Allee, space was left in the middle of the platform area for another track.

Construction began in May 1912 to replace the triangular junction with two lines built as a grade-separated cross with a new Gleisdreieck interchange station at the intersection.

In 1944, as the air raids continued, the Berliner Verkehrsbetriebe had trouble keeping the U2 line in operation, as many stations were affected such as Gleisdreieck, Nollendorfplatz, Olympiastadion, Potsdamer Platz, and Klosterstraße.

As a consequence of the experience of 17 June, the Western BVG established a new route of the AII from Krumme Lanke to Kottbusser Tor which was independent of East Berlin, but which was soon abandoned.

On the orders of the then GDR Interior Minister Karl Maron, trains on the section of line A (now U2) in East Berlin terminated at Thälmannplatz station (now Mohrenstraße).

The stations of Stadtmitte, Hausvogteiplatz, Spittelmarkt, Rosa Luxemburg-Platz and Senefelderplatz were remodelled and given new wall tiles in the 1960s, all for show, as U6 ran through without stopping.

In 1987, the stations of Markisches Museum and Klosterstraße were remodelled, as part of the rebuilding for the celebration of 750th anniversary of Berlin, with artistic representations of the urban development of historic buses and trams instead of advertising space that is typically found in non-socialist economic systems.

In order to increase the attractiveness of the two markets, the BVG established a shuttle service of museum trams on the elevated railway in August 1978.

The tracks, excluding the section between the U-Bahn stations of Bülowstraße and Potsdamer Platz, which was being used for other purposes (markets and storage facilities), were equipped with inductive loops for this experiment.

The Senate planned to convert the small profile network of the U-Bahn to magnetic levitation, but this raised considerable concerns in the BVG.

On 19 December 1988, there was an accident at the terminal station of Kemperplatz due to an operating error with the control system when an unoccupied M-Bahn test train went beyond the end of the track, broke through a glass wall and got stuck 6 metres (19 ft 8 in) above the ground.

Just two weeks later, the M-Bahn had to stop operating to make room for construction work to reopen the section of the U2 U-Bahn line that had been closed 30 years earlier.

The BVG, on the order of the senator responsible for transport matters, renamed the elevated station after the street opposite, even though Eberswalder Straße was much less significant.

Extremely difficult ground conditions, the high water table and the discovery of a medieval settlement slowed progress significantly.

During the construction, a generous entrance building was built at the same time with a lift and escalators to provided convenient connections to S-Bahn line S2 to Bernau.

In addition to new platform slabs and the refurbishment of the entrance building, it received two lifts that can be reached by an independent bridge from the station forecourt.

The window gallery has been reopened there and the walls at the rear of the track have been decorated with newly fired ceramic tiles displaying various historical cityscapes.

In addition, the BVG found in 2005 that a bridge between the Gleisdreieck and Bülowstraße stations, which dates back to the early days of the Berlin U-Bahn and was not renovated after German reunification has been significantly damaged.

Other projects, such as the modernisation of the U1 elevated line or Jannowitzbrücke station were delayed due to the €8 million renovation that had not been included in the BVG budget.

In recent years Schönhauser Allee, Märkisches Museum, Alexanderplatz, Stadtmitte, Gleisdreieck, Theodor-Heuss-Platz, Olympia-Stadion and, in early 2009, Potsdamer Platz station, which is very important for tourists, have been given a lift.