along the Amiens–Roye road, allowing the two armies to cooperate. The Picardy terrain provided a good surface for tanks, unlike in Flanders, and the defences of the German 2nd Army under General Georg von der Marwitz were relatively weak, having been subjected to continual raiding by the Australians in a process termed peaceful penetration. Battles Advance in Picardy Battle of Amiens The Battle of Amiens (with the French attack on the southern flank called the Battle of Montdidier) opened on 8 August, with an attack by more than 10 Allied divisions—Australian, Canadian, British and French forces—with more than 500 tanks. Through careful preparation, the Allies achieved surprise. 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 wide had been created in the German line south of the Somme. The Allies had taken 17,000 prisoners and 339 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". 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. During those three days, the Allies had managed to gain . Most of this was taken on the first day as the arrival of German reinforcements after this slowed the Allied advance. 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. Somme On 15 August, Foch demanded that Haig continue the Amiens offensive, even though the attack was faltering as the troops outran their supplies and artillery and German reserves were being moved to the sector. Haig refused and prepared to launch a fresh offensive by the Third Army at Albert (the Battle of Albert), which opened on 21 August. The offensive was a success, pushing the German 2nd Army back over a front. Albert was captured on 22 August. The attack was widened on the south, by the French Tenth Army starting the Second Battle of Noyon on 17 August, capturing the town of Noyon on 29 August. On 26 August, to the north of