The Metz fortifications contributed some of their long 100mm guns to replace the short 100mm guns at Thionville when France upgraded the Thionville sector to back up the Maginot Line fortifications in the area. Fort Jeanne d'Arc was the headquarters for the French 3rd Army in 1940. During the Battle of France the Metz area was bypassed and encircled by German forces, with the Maginot and earlier fortifications seeing little action before the Armistice of 1940.