[1] When World War II reached Norway in 1940, Johnsen participated in the Battle of Bagn.
He joined the Norwegian Independent Company 1, and served on a motor torpedo boat from May to December 1944, and was parachuted to Norway in early 1945.
[4] He met his wife in the United Kingdom in 1944,[5] Birgit "Tullen" Lützow-Holm.
She worked as a secretary at the intelligence office FO II in London during the war,[6] and she was decorated with the Defence Medal 1940–1945.
[1] He held the rank of captain, advanced to lieutenant colonel in 1958 and major general in 1972.