United Nations Operation in the Congo
He was a colonel and commander of the twelfth and fourteenth Swedish UN battalion in Congo from 1961 to 1962. At the same time, he was brigade commander of the Swedish, Indian and Irish troops in southern Katanga, which was part of the United Nations Operation in the Congo (ONUC) from June 1961 to May 1962. Wærn was the section chief of the IV Military Commanding Staff in 1962 and was commander of the Swedish UN Battalion in Cyprus in 1964, part of the United Nations Peacekeeping Force in Cyprus (UNFICYP). He was infantry commander of the Stockholm Coastal Artillery Defense ("Stockholms kustartilleriförsvar") in 1966.