In September 1939, with the arrival of the reserves, the battalions of the 23rd Fortress Infantry Regiment (23e RIF), served each in a chain link to form new Fortress infantry regiments of « mobilization », Bigeard was assigned to the 79th Fortress Infantry Regiment () in the under fortified sector of Hoffen and the Maginot Line. Volunteer for the franc corps, he led a combat group at Trimbach in Alsace and became quickly a sergent-chef then adjudant (warrant officer) at the age of 24.