U-55 may refer to one of the following German submarines:
- SM U-55, a Type U 51 submarine launched in 1916 and that served in the First World War until surrendered 26 November 1918; in service as Japanese submarine O-3, 1920–21; dismantled at Sasebo, March–June 1921; briefly recommissioned as Auxiliary Vessel No. 2538, 1923
- During the First World War, Germany also had these submarines with similar names:
- SM UB-55, a Type UB III submarine launched in 1917 and sunk on 23 April 1918
- SM UC-55, a Type UC II submarine launched in 1916 and sunk on 29 September 1917
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-55 (1939), a Type VIIB submarine that served in the Second World War until sunk 30 January 1940
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.