The U3 is a line of the Hamburg U-Bahn. The ring line with a length of serves 25 stations. The first part opened in 1912. The line starts in Wandsbek-Gartenstadt and leads via Barmbek into the ring passing through the city centre and back to Barmbek.
The ring line was built from 1906 to 1912 and had a length of and with 23 stations. The first part of the line which was first opened in February 1912, was the part between Rathaus via Hauptbahnhof and to Barmbek. On 2 January 1967, the first part of the line to Billstedt opened with the section leading to Horner Rennbahn. Since then, the U3 line was not a ring line anymore until the year of 2009.
In 2009, eastern parts of U2 and U3 lines were swapped behind Berliner Tor. Before that, the U2 line led to Wandsbek-Gartenstadt. Since then, it ends in Mümmelmannsberg, and the U3 became a ring line again with a branch to Wandsbek-Gartenstadt.
A new Fuhlsbüttler StraÃÂe station is planned between Barmbek and HabichtstraÃÂe stations, the construction of which would begin in 2027. It is expected to be completed in 2029.