German submarine U-121
U-121 may refer to one of the following German submarines:
- SM U-121, a Type UE II submarine launched in 1918 and that served in World War I; surrendered to France; sunk as target on 1 July 1921
- During World War I, Germany also had this submarine with a similar name:
- SM UB-121, a Type UB III submarine launched in 1918 and surrendered in 1918
- During World War I, Germany also had this submarine with a similar name:
- German submarine U-121 (1940), a Type IIB submarine that served in World War II and was scuttled on 2 May 1945