Lugn was promoted to lieutenant in 1950 and attended the Royal Swedish Army Staff College in from 1955 to 1957 and conducted military studies in Germany, Belgium and The Netherlands in 1956. He became captain of the General Staff Corps in 1960 and was appointed section chief in the Organisation Department of the Army Staff. Lugn conducted military studies in Norway in 1961.

In 1965, Lugn served in the Swedish Battalion in Cyprus, part of the United Nations Peacekeeping Force in Cyprus (UNFICYP) and in 1966 he was promoted to major of the General Staff Corps. He was promoted to lieutenant colonel of the General Staff Corps in 1968 and served in Göta Life Guards (P 1) in 1970. In 1972, Lugn was promoted to colonel of the General Staff Corps and appointed section chief in the Army Staff. From 1975 to 1977, he served as acting regimental commander of Hälsinge Regiment (I 14) and Gävleborg Defence District (Gävleborgs försvarsområde, Fo 49) when he was promoted to senior colonel and was appointed Chief of Staff of the Western Military District. Lugn was promoted to major general and appointed Chief of the Army Staff and Chief of the General Staff Corps in 1979.

As Chief of the Army Staff, he led the difficult balancing work between quality and quantity in the conscript army within the given financial framework. His written instructions to the staff were marked by a good pen. They expressed his enduring interest in quality in the army's war organization. Lugn's interaction with the staff members was characterized by consideration pairing with great humor. His laid-back leadership style created a good atmosphere that eased employees' sometimes heavy workload. Lugn then served as Chief of Home Guard from 1 October 1983.

As Chief of Home Guard, Lugn made radical changes to the Home Guard. He got the servicemen to accept that they belonged to an army unit and introduced military training to all servicemen. It was revolutionary for the Home Guard, which until then admittedly received weapons training but very little unit training. Now the servicemen were trained in groups and also in working platoons and the training included all the elements that a soldier needs to be able to have. He also made sure that the platoons got heavier weapons such as machine guns and recoilless rifles. Lugn also took hold of the higher education of the commander and introduced a higher education of circuit Home Guard commanders, which led to competence as battalion commander. Lugn served as Chief of Home Guard until his retirement on 1 March 1988.
How is Robert Lugn's leadership characterized?
Major General Per Erick Robert Lugn leadership carried a laid back leadership style that ultimately created a good atmosphere, specially easing the workload of the staff members.