German submarine U-99

U-99 may refer to one of the following German submarines:


 * SMU U-99, a Type Mittel U submarine launched in 1917 and that served in the First World War until sunk on 7 July 1917
 * During the First World War, Germany also had these submarines with similar names:
 * SMU UB-99, a Type UB III submarine launched in 1918 and surrendered on 26 November 1918; became French submarine [[French submarine Carissan|''Carissan}} until 24 July 1935; broken up
 * SMU UC-99, a Type UC III submarine launched in 1918 and surrendered on 22 November 1918; served as Japanese submarine ''O-5}}, 1920–21; broken up at [[Yokosuka Navy Yard between March and June 1921; destroyed as target, October 1921


 * GS U-99 (1940), a Type VIIB submarine that served in the Second World War until sunk on 17 March 1941