 The offensive began on 8 August 1918 when 20 Allied divisions , including four Australian , struck at Amiens on the Somme . Using the combined arms techniques developed earlier at Hamel , the Allies achieved territorial gains that had been unheard of since the start of the war . In the Australian sector , the 4th and 5th Divisions had initially spearheaded the advance , before the 2nd and 3rd Divisions had advanced another three kilometres to secure the secondary objectives . The attack had been so successful that it was later described by German General Erich Ludendorff as a " black day " for the German Army . 
