Hundred Days Offensive - Wikipedia

On August 8, 1918, during World War I, the Allies launched the Hundred Days Offensive, beginning with the Battle of Amiens where 500 tanks and 10 Allied divisions attacked German lines. From the article:

"The Battle of Amiens (with the French attack on the southern flank called the Battle of Montdidier) opened on 8 August 1918, with an attack by more than 10 Allied divisions—Australian, Canadian, British and French forces—with more than 500 tanks.[9]:497 Through careful preparation, the Allies achieved surprise.[10]:20,95[11] The attack, led by the British Fourth Army, broke through the German lines and tanks attacked German rear positions, sowing panic and confusion. By the end of the day, a gap 15 mi (24 km) wide had been created in the German line south of the Somme.[12] The Allies had taken 17,000 prisoners and 330 guns. Total German losses were estimated to be 30,000 men, while the Allies had suffered about 6,500 killed, wounded and missing. The collapse in German morale led Erich Ludendorff to dub it "the Black Day of the German Army".[10]:20,95

The advance continued for three more days but without the spectacular results of 8 August, since the rapid advance outran the supporting artillery and ran short of supplies.[13] During those three days, the Allies had managed to gain 12 mi (19 km). Most of this was taken on the first day as the arrival of German reinforcements after this slowed the Allied advance.[14] On 10 August, the Germans began to pull out of the salient that they had managed to occupy during Operation Michael in March, back towards the Hindenburg Line."