In July 1936, the outbreak of the Spanish Civil War gave Bethune the opportunity to fight for the communist cause and against fascism. This was a conflict between the Republicans Loyalists duly elected by the Spanish population and the fascists led by Franco, and supported by Hitler, Mussolini and, many say, the Spanish Catholic Church. Bethune viewed the conflict as a matter of ‘Republican good versus Fascist evil’.
With some prominent Canadian antifascists, he helped form the Committee to Aid Spanish Democracy and, in late October 1936, sailed from Quebec City to Spain. Once in Madrid, he quickly realized that the Republican forces needed a blood transfusion service and a blood bank, a concept that he had likely learned from Archibald, who had himself used blood transfusions during World War I.
When the Spanish authorities received his ideas with great enthusiasm, he left for France and England to buy equipment and learn the latest techniques in blood typing, storage and transfusions. On his return to Spain, he designed a mobile transfusion vehicle that incorporated a refrigerator, a sterilizing unit and an incubator. The unit, called Servicio Canadiense de Transfusion de Sangre Al Fiente also contained equipment and containers for drawing and giving blood transfusions on the battlefield.