Gilbert was conscripted into military service in May 1951, after working for eight months as an apprentice electrician.

During the Korean War, Soldat de 1re Classe Gilbert Hauffels served in the second contingent as an Light Machine Gun (LMG) gunner. In an interview recorded in 2018, Gilbert stated that he was mostly driven by his youthful spirit of adventure as well as ideological determination to oppose communism. Gilbert's diary is one of the best preserved sources portraying the soldier's everyday life in Korea, namely artillery duels with the Chinese and seemingly never-ending fortification work in extreme heat.

Upon his return from Korea, Gilbert initially attempted to further his military career but in 1956, he decided to work for the customs (Douanes). During his deployment, Gilbert developed an interest in the country and its culture which led him to visit South Korea on several occasions. From 1981 to 2015, he was the secretary and until now the president of the Luxembourg Korean Association.