he left the swedish army in 1939 and joined the finnish army during the winter war as part of the swedish volunteer corps. åkerman was promoted to major in the finnish army and then lieutenant colonel in 1940. he was then again major of the swedish general staff corps in 1940. åkerman was again teacher at the royal swedish air force staff college from 1941 to 1942 and strategy teacher at the royal swedish army staff college from 1940 to 1942. he became a lieutenant colonel in 1941 and colonel in 1943.