U-27 may refer to one of the following German submarines:
- SM U-27 (Germany), was the lead ship of the Type U 27 class of submarines; launched in 1913 and served in the First World War until sunk on 19 August 1915; the events surrounding U-27's sinking are known as the Baralong Incident
- During the First World War, Germany also had these submarines with similar names:
- SM UB-27, a Type UB II submarine launched in 1915 and sunk on 27 July 1917
- SM UC-27, a Type UC II submarine launched in 1916 and surrendered on 3 February 1919
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-27 (1936), a Type VIIA submarine that served in the Second World War until sunk on 20 September 1939
- German submarine U-27 (S176), a Type 206 submarine of the Bundesmarine that was launched in 1974 and scrapped in 1996
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.