The same year he was promoted to captain in the Swedish Army and did the certificate exams for balloon license.

[4] Petersén participated in the Finnish Civil War in 1918 as a lieutenant colonel in the White Guard.

[7] During the war, Petersén and his colleague Algot Törneman had organised private arms trades.

They had sold weapons via a private firm, Skandiastål, to the Norwegian and Danish resistance movements.

[14][15] Esther was adopted by her stepfather Carl Warodell (1847–1902), a captain of the Göte Life Guards.