U-43 may refer to one of the following German submarines:
- SM U-43 (Germany), the lead ship of the Type U 43 class of submarines; launched in 1914 and that served in the First World War until surrendered on 20 November 1918
- During the First World War, Germany also had these submarines with similar names:
- SM UB-43, a Type UB II submarine launched in 1916; transferred to Austria-Hungary and renamed U-43; surrendered on 6 November 1918
- SM UC-43, a Type UC II submarine launched in 1916 and sunk on 10 March 1917
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-43 (1939), a Type IX submarine that served in the Second World War until sunk on 30 July 1943
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.