Henri's voluntary military service started in 1948. On 26 February 1948, he joined the Ist Battalion before being transferred to the military police section of the Luxembourg City garrison in May. His entire military career was marked by switches back and forth between the school to become a Caporal on the one hand and the military police unit of Luxembourg City on the other. After his promotion to Caporal de Réserve in November 1948, he was released from active duty. Upon his reenlistment in February 1949, the military administration reinstated him as a Soldat de 1re Classe and revoked his previously obtained rank of Caporal de Réserve.

Before he volunteered to fight in Korea, Henri managed to regain his former rank of Caporal in May 1950. Sadly, only very little is known about his Korea deployment. 

After he returned home, he joined the IInd Battalion and reenlisted for another two years. Because of his military police experience, he was transferred to the D.A.L. (Douanes et Accises Luxembourg) in March 1952. He later joined the Gendarmerie of Luxembourg City, where he had applied as a police officer. Passing the exam on 8 May 1952, he was stationed at Oberpallen. As a result, the army released him on military leave on 1 October 1953 so that he could follow his civilian career in the service of law enforcement.