German submarine U-109

U-109 may refer to one of the following German submarines:


 * SMU 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:
 * SMU UB-109, a Type UB III submarine launched in 1917 and sank in 1918
 * GS U-109 (1940), a Type IXB submarine that served in the Second World War and sank in 1943