he was then attaché in warsaw from 1919 to 1920, was in the commission concerning the exchange of greek and turkish populations from 1923 to 1925, the bulgarian refugee commission from 1926 to 1928, in syria in 1929 and the league of nations border control commission in syria and iran in 1932. in 1932, petersén was promoted to major in the swedish army. he was head of department at the international red cross in paris from 1921 to 1937, the general secretary of the royal swedish aero club from 1937 to 1939 and was legation counsellor in berlin and worked at the b department of the ministry for foreign affairs from 1939 to 1940. petersén was head of the intelligence agency c-byrån from 1940 to 1946. in 1944, he led the swedish side of the operation stella polaris.