Built in late 1916, the Hindenburg Line—named by the British for the German commander in chief, Paul von Hindenburg; it was known to the Germans as the Siegfried Line—was a heavily fortified zone running several miles behind the active front between the north coast of France and Verdun, near the border of France and Belgium. By September 1918, the formidable system consisted of six defensive lines, forming a zone some 6,000 yards deep, ribbed with lengths of barbed wire and dotted with concrete emplacements, or firing positions. Though the entire line was heavily fortified, its southern part was most vulnerable to attack, as it included the St. Quentin Canal and was not out of sight from artillery observation by the enemy. Also, the whole system was laid out linearly, as opposed to newer constructions that had adapted to more recent developments in firepower and were built with scattered "strong points" laid out like a checkerboard to enhance the intensity of artillery fire.
The Allies would use these vulnerabilities to their advantage, concentrating all the force built up during their so-called "Hundred Days Offensive"—kicked off on August 8, 1918, with a decisive victory at Amiens, France—against the Hindenburg Line in late September. Australian, British, French and American forces participated in the attack on the line, which began with the marathon bombardment, using 1,637 guns along a 10,000-yard-long front. In the last 24 hours the British artillery fired a record 945,052 shells. After capturing the St. Quentin Canal with a creeping barrage of fire—126 shells for each 500 yards of German trench over an eight-hour period—the Allies were able to successfully breach the Hindenburg Line on September 29.
The offensive was driven ahead by Australian and U.S. troops, who attacked the heavily fortified town of Bellicourt with tank, aircraft and artillery support. After four days of battle, with heavy losses on both sides, the Germans were forced to retreat. With Kaiser Wilhelm II pressured by the military into accepting governmental reform and Germany’s ally, Bulgaria, suing for an armistice by the end of September, the Central Powers were in disarray on the battlefield as well as the home front. The Allies, meanwhile, pressed their advantage on the Western Front throughout the following month, which would, against their predictions, turn out to be the final month of World War I.