By their ultimate failure in the Second Battle of the Marne (15 July - 6 August 1918) the Germans had been definitely thrown back on the defensive and were faced with the possibility of having to seek a line of resistance further east than Bapaume.
He was also urgently and instantly compelled to expedite his withdrawal from his positions about Serre, where, as a result of Rawlinson's advance south of the Somme, he was being confined into a dangerous salient. He no doubt meditated an orderly movement as in the early months of 1917. Foch and Haig did not, however, mean to let him go so lightly, but to force on him a disorganised retreat. Moreover, in the Amiens area his troops had by this time been heavily reinforced, and there the wire and trenches of the old Somme battlefield would make a continuance of our attack costly. For these reasons, therefore, Haig broke off the battle on the Fourth Army front and transferred it to the Bapaume sector north of the river, with the object of turning the line of the old Somme defences from the north and of preventing the enemy's destruction of road and rail communications in his withdrawal on Bapaume.
The initial stage of the Third Army attack was fixed for 21st August. The objective aimed at for that day was the Albert-Arras railway. The 22nd would see the Fourth Army conform on the right by the capture of Albert and by the passage of the lower valley of the Ancre, while the Third Army brought forward troops and guns into position for the main blow. This would be delivered on 23rd August by the Third Army and by the left wing of the Fourth north of the Somme, while the remainder of the Fourth south of the river would advance to establish a protecting flank.
In the first stage, the New Zealand Division would support the main attack by artillery and machine gun fire, and by advancing in conformity with the 37th Division to a "Blue" Line on the eastern outskirts of Puisieux and the high ground southwards beyond Serre overlooking the Ancre.
Then the plan was to encircle Bapaume, where 4 great highways run, 1 southwest to Albert, 1 south-east to Péronne, 1 eastwards towards Cambrai, and 1 northwards towards Arras. But it turned out that the Germans held Bapaume only for such time as would suffice to cover his retirement on the Hindenburg Line. When the progress made in the Battle of the Searpe (begun 26th August) proved a menace to its northern pivot, he hesitated no longer.
By 27th August the enemy, threatened by the progress of the Third Army, had fallen back on the whole of his front in the south between the Oise and the Somme. But despite German science and stubbornness there could be no doubt as to the satisfactory results of the battle. "The troops of the Third and Fourth Armies, comprising 23 British Divisions, by skillful leading, hard fighting, and relentless and unremitting pursuit, had driven 35 German Divisions from one side of the old Somme battlefield to the other, thereby turning the line of the River Somme. In so doing they had inflicted upon the enemy the heaviest losses in killed and wounded, and had taken from him over 34,000 prisoners and 270 guns." The IV. Corps alone had captured nearly 8000 prisoners. Of these the New Zealanders' share amounted to 47 officers and just over 1,600 men.