Rapp was appointed Vice Chief of the Royal Swedish Air Force Materiel Administration and became a member of the board of the Swedish National Defence Research Institute on 1 October 1957. He was promoted to lieutenant general and became Chief of the Air Force on 15 January (took office 1 July) 1960. He was promoted to general and was Supreme Commander of the Swedish Armed Forces from 10 March (took office 1 October) 1961. During his time on the post, major changes were made to the Swedish defense, including an enhanced coordination between the army, the air force and the navy. The reorganization also meant that the Supreme Commander was given greater responsibility. Rapp left the post on 30 September 1970 and he was then general in the Swedish Air Force reserve from 1 October 1970 to 1981.