petersén was born in stockholm, sweden, the son of deputy assistant carl petersén and ingeborg tanberg. he became a second lieutenant in the uppland artillery regiment (a 5) in 1903 and attended the gymnastic central institute in 1907. petersén was major and instructor in the persian gendarmerie from 1911 to 1913 and participated in the gallipoli campaign in 1915. the same year he was promoted to captain in the swedish army and did the certificate exams for balloon license. petersén participated in the finnish civil war in 1918 as a lieutenant colonel in the white guard.