When World War II reached Norway on 9 April 1940, with the German invasion, he volunteered and fought for Norway in the ensuing battles. He joined Norwegian forces for the first time at Voss and fought in Hallingdal. After the capitulation of the regular Norwegian forces, he joined the secret resistance movement as a member of Milorg. Later he became the leader of Milorg., Bergen District, from 15 May 1943 until 26 February 1944 when he left the country.