Garde suisse
From 1975 through 1976, Estermann attended the officer training school for the Swiss Army at Thun. He subsequently reached the rank of lieutenant as a Swiss reserve officer. In 1977 Estermann served briefly in the Pontifical Swiss Guard at the Vatican. He then lived in Argentina for two years. In July 1980 he rejoined the Swiss Guard as an officer, thereafter receiving promotions to Major (1983) and then to Lieutenant Colonel (1987). In 1988 he was appointed Commander of the Swiss Guard.