U-1 may refer to one of the following German submarines:
(1906), Germany's first U-boat, now preserved in the Deutsches Museum in Munich; served in the First World War as a German training submarine for the Kaiserliche Marine; now a museum ship During the First World War, Germany also had these submarines with similar names: , a Type UB I submarine launched in 1915; transferred to Austria-Hungary on 12 July 1915 and renamed U-10; sunk on 9 July 1918 , a Type UC I submarine launched in 1915 and sunk in July 1917 , a Type IIA submarine that served in the Second World War and was sunk in April 1940 , a Type 201 submarine of the Bundesmarine, launched in 1961 and scrapped in 1967 , a Type 205 submarine of the Bundesmarine that was launched in 1967 and sold in 1991
U-1 or U-I may also refer to: , lead boat of the for the Austro-Hungarian Navy