U-33 may refer to one of the following German submarines:
- SM U-33 (Germany), was a Type U 31 submarine launched in 1914 and that served in the First World War until surrendered on 16 January 1919
- During the First World War, Germany also had these submarines with similar names:
- SM UB-33, a Type UB II submarine launched in 1915 and sunk on 11 April 1918
- SM UC-33, a Type UC II submarine launched in 1916 and sunk on 26 September 1917
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-33 (1936), a Type VIIA submarine that served in the Second World War until sunk on 12 February 1940
- German submarine U-33 (S183), a Type 212 submarine of the Bundesmarine that was launched in 2004 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.