defensive barrier improvised by the German army on the Western Front in World War I. Faced with substantial numerical inferiority and a dwindling firepower advantage, the new German commanders, Field Marshal Paul von Hindenburg and Gen. Erich Ludendorff, shortened their lines and installed concrete pillboxes armed with machine guns as the start of an extended defensive system up to eight miles deep, based on a combination of firepower and counterattacks. The Hindenburg Line resisted all Allied attacks in 1917 and was not breached until late in 1918.