U-109 may refer to one of the following German submarines:
- SM U-109, a Type U 93 submarine launched in 1917 that served in the First World War and sank in 1918
- During the First World War, Germany also had this submarine with a similar name:
- SM UB-109, a Type UB III submarine launched in 1917 and sank in 1918
- During the First World War, Germany also had this submarine with a similar name:
- German submarine U-109 (1940), a Type IXB submarine that served in the Second World War and sank in 1943
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.