A small number of Australian volunteers fought on both sides of the Spanish Civil War , although they predominantly supported the Spanish Republic through the International Brigades . The Australians were subsequently allocated to the battalions of other nationalities , such as the British Battalion and the Lincoln Battalion , rather than forming their own units . Most were radicals motivated by ideological reasons , while a number were Spanish @-@ born migrants who returned to fight in their country of origin . At least 66 Australians volunteered , with only one — Nugent Bull , a conservative catholic who was later killed serving in the RAF during the Second World War — known to have fought for General Francisco Franco 's Nationalist forces .