[1] During the occupation of Norway by Nazi Germany, he became involved in the Norwegian resistance movement.
[5] After the liberation of Norway in May 1945, when Aks 13000 became Sentralledelsens Aksjonskommando under the temporary Home Front rule, Giertsen continued to serve.
[6] Without payment he performed medical checks of all sabotage personnel in the district, at a hotel in Frogner together with Ole Øyseth.
[7] Giertsen also continued his physician career, and worked part-time in the companies Fred.
Olsen & Co. from 1935 to 1947, Aftenposten from 1945 to 1973, Esso Norway from 1945 to 1955, Leif Höegh & Co from 1955 to 1975 as well as the Norwegian royal court administration from 1945 to 1984.