Spain
- Hugh Dubh O'Neill
- Shane O'Neill (son of Hugh)
- Field Marshal Alejandro O'Reilly
- Juan O'Donojú
- Joaquín Blake y Joyes
- Ricardo Wall
- Leopoldo O'Donnell y Jorris
- Carlos Luis O'Donnell y Jorris
- Ambrosio O'Higgins
Spanish Civil War
- Frank Ryan
- Eoin O'Duffy
Read more about this topic: Irish Military Diaspora