German submarine U-40 may refer to one of the following German submarines:
- SM U-40 (Germany), was a Type U 31 submarine launched in 1914 and that served in the First World War until sunk 23 June 1915
- During the First World War, Germany also had these submarines with similar names:
- SM UB-40, a Type UB II submarine launched in 1916 and scuttled on 5 October 1918
- SM UC-40, a Type UC II submarine launched in 1916 and sunk on 21 January 1919 while on way to surrender
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-40 (1938), a Type IX submarine that served in the Second World War until sunk on 13 October 1939
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.