U-34 may refer to one of the following German submarines:
- SM U-34, was a Type U 31 submarine launched in 1914 and that served in the First World War; disappeared after 18 October 1918
- During the First World War, Germany also had these submarines with similar names:
- SM UB-34, a Type UB II submarine launched in 1915 and surrendered on 26 November 1918
- SM UC-34, a Type UC II submarine launched in 1916 and scuttled on 30 October 1918
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-34 (1936), a Type VIIA submarine that served in the Second World War until sunk on 5 August 1943
- German submarine U-34 (S184), a Type 212 submarine of the Bundesmarine that was launched in 2006 and in active service
This article includes a list of ships with the same or similar names. If an internal link for a specific ship led you here, you may wish to change the link to point directly to the intended ship article, if one exists.