Nicolas Karrenberg was born on 23 April 1924 in Esch-sur-Alzette and held dual nationality: Luxembourgish and German. He voluntarily joined the Wehrmacht in Spring 1942 and was officially recruited on 17 October 1942. About seven months later, on May 15, 1943, he left his military duty while on leave. He fled to France, where he claimed to have joined the Maquis. Between January 1945 and July 1945, he reportedly fought on the Allied side within the American Army.
His desertion led to his family members, including his parents and five siblings, being forcibly relocated to resettlement camps in Lower Silesia on 2 July 1943. After being transferred to six different camps, they finally returned to Luxembourg in May 1945. Nikolas Karrenberg himself came back to Luxembourg on 12 July 1945, and faced trial as a voluntary enlistee. According to the District Court of Luxembourg (1952), his decision to join the Wehrmacht was driven by a sense of adventure rather than pro-German sentiment. Moreover, it provided an opportunity for him to escape difficult circumstances at home. In 1948, he made the voluntary choice to join the French Foreign Legion and served in Indochina until 1952.