The "Mac-Paps" were a unit of the International Brigades, a volunteer force recruited world-wide to oppose the fascist forces bent on overthrowing the government of Spain. Formed in Spain in 1937, the battalion was named for the leaders of the 1837 rebellions in Upper and Lower Canada. Despite their government's opposition, more than 1500 Canadians volunteered to fight with the Republican forces in the Spanish Civil War. They fought courageously for their ideals, suffering heavy losses in major battles. About half survived to return home in 1939.