During World War II Hagen took the Free French side and was part of the first New Caledonian volunteer contingent to sail to Europe.
He served in France, Italy and North Africa, rising to become a lieutenant by the end of the war.
[1] He later became the Nouméa manager of Pan American Airways, and was promoted to captain in the army reserves.
He was re-elected in 1957 (when the General Council was renamed the Territorial Assembly) as a member of the National Centre of Social Republicans.
Although the results of the South constituency were annulled in June, he was re-elected in the subsequent by-election in November.