Ludendorff called August 8, 1918 'the Black Day of the German Army' — the day 500 tanks punched a 15-mile hole in German lines and the 95 days that ended the war began.
The Hundred Days Offensive began August 8, 1918, at Amiens with a surprise assault that became one of the most decisive single days of the war. Over 500 tanks advanced behind a rolling artillery barrage and thick morning fog, catching German forces completely off guard. By day's end, Allied forces had opened a 15-mile gap and captured 17,000 prisoners. General Ludendorff called it 'the Black Day of the German Army.'
The offensive combined everything the Allies had learned over four years of war: massed tanks, coordinated infantry, rolling artillery barrages, close air support, and strategic surprise. It was the realization of combined-arms doctrine glimpsed at Cambrai in 1917 — now executed at scale with experienced troops, overwhelming resources, and an enemy that had spent its last reserves in the failed Spring Offensive.
The Hindenburg Line — Germany's most formidable defensive system, a network of trenches, bunkers, and tunnels that German commanders considered impregnable — was breached on September 29. Allied forces crossed the St. Quentin Canal, where German planners had assumed the water obstacle would halt any assault. The psychological effect on the German High Command was catastrophic.
As German lines crumbled, Berlin collapsed alongside them. General Ludendorff suffered a breakdown in late September and resigned in October. Kaiser Wilhelm II abdicated November 9. The government that signed the armistice was a brand-new civilian administration — a transfer of power the German military would later weaponize, claiming they had been 'stabbed in the back' by politicians while the army was still in the field.
American forces played a growing role through the Meuse-Argonne Offensive, which from late September involved 1.2 million U.S. soldiers pushing through the most heavily fortified terrain on the Western Front. The sheer weight of American manpower — fresh, well-supplied, and arriving at rates Germany could never match — ground down resistance across a 200-mile front simultaneously.
The Hundred Days ended not with a climactic final battle but with an armistice on November 11, when German forces were retreating but had not completely collapsed. The last man killed in World War I was Private Henry Gunther, shot at 10:59 a.m. — one minute before the ceasefire — still advancing on German lines even as German soldiers, knowing the armistice was seconds away, were waving him back.