The first part of the line was opened on 1 December 1914 from Kellinghusenstraße to Ohlsdorf with electric service. In 1920, the new branch from Wandsbek-Gartenstadt (Walddörfer railway) to Volksdorf opened; the two branches from here to Großhansdorf and to Ohlstedt followed in 1921 and 1925. Also in 1921, the Langenhorn railway to Ochsenzoll was established. On this line, there had been a preliminary service with steam trains since 1918.

On 2 June 1929 the first part and on 25 March 1931 the second part of the KellJung line to Jungfernstieg was added. From 1960 to 1963 the line was built through the city center to Wandsbek-Gartenstadt, which completed the U1 line, connecting the branch to Volksdorf. In 1969 the Langenhorn railway was extended to Garstedt and in 1996 to Norderstedt Mitte.

• 1 December 1914: Kellinghusenstraße − Ohlsdorf
• 12 September 1918 - 22 May 1919 (powered by steam); 6 September 1920 (powered by electricity): Wandsbek-Gartenstadt – Volksdorf (Walddörfer railway, Walddörferbahn)
• 1 July 1921: Ohlsdorf − Ochsenzoll (Langenhorn railway)
• 5 November 1921: Volksdorf − Großhansdorf (then: Groß Hansdorf) (Walddörferbahn)
• 1 February 1925: Volksdorf − Ohlstedt (Walddörferbahn)
• 2 June 1929: Kellinghusenstraße − Stephansplatz (KellJung line)
• 25 March 1931: Stephansplatz − Jungfernstieg
• 22 February 1960: Jungfernstieg − Meßberg
• 2 October 1960: Meßberg − Hauptbahnhof Süd (then: Hauptbahnhof)
• 2 July 1961: Hauptbahnhof Süd (then: Hauptbahnhof) − Lübecker Straße
• 1 October 1961: Lübecker Straße − Wartenau
• 28 October 1962: Wartenau − Wandsbek Markt
• 3 March 1963: Wandsbek Markt − Straßburger Straße
• 4 August 1963: Straßburger Straße − Wandsbek-Gartenstadt
• 1 June 1969: Ochsenzoll − Garstedt
• 28 September 1996: Garstedt − Norderstedt Mitte

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  Ochsenzoll
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  Ohlsdorf
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  Kellinghusenstraße
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  Volksdorf