U-3 may refer to one of the following German submarines:
, lead boat of the Type U 3 submarines; launched in 1909 and served in the First World War as a training submarine; surrendered in 1918 During the First World War, Germany also had these submarines with similar names: , a Type UB I submarine launched in 1915 and sunk on 23 May 1915 , a Type UC I submarine launched in 1915 and sunk on 27 May 1916 , a Type IIA submarine that served in the Second World War and was scrapped in 1945 , a Type 201 submarine of the Bundesmarine that was launched in 1964; loaned out to Royal Norwegian Navy from 1964 to 1966; later broken up
U-3 or U-III may also refer to: , lead boat of the for the Austro-Hungarian Navy
See also U-3 (disambiguation)