Under the influence of his father, he founded a communist youth group at the age of 16. This led to an arrest and a stay in prison. After his release, Mohren joined the Aachen Combat League against Fascism. Since the beginning of the war, he and like-minded friends had followed events via BBC Radio. He was fascinated by the direct reporting, which also called for withholding any support for Hitler's war machine. As a result, Josef decided to work only in the materials distribution section at the Gouley mine, in order to avoid coal production and his conscription into the army.
On November 17, 1944, the Ravelsberg is littered with mines. It is here that Josef Mohren starts recovering the bodies of dead American soldiers. He ensures they received an honorable burial. For him, they represented idealism and a steadfast commitment to freedom. In the first three weeks, he initially recoveres 32 American soldiers, but eventually also 132 fallen German soldiers. Josef Mohren survived and became a special constable, with the aim of helping prevent any resurgence of fascism.