From July, the British started a three phase thrust through the strongly defended German lines in the Somme. Preliminary attacks were made in the beginning of September to afford suitable assault positions or to deny observation.
The NZ Division, who were to be included in the main operation, phase three, were recuperating from work on the Lys, in the lower vallies of he Somme. Then on the 27th of August, troops filtered through Bonnay, Dernacourt, Fricourt and the reverse slopes of Montuaban in order to reach trench systems around Deville & High Woods. All the while, the sound of artillery growing louder.
"Long here now the Fourth Army plans had been crystallized. While the French would continue their pressure on the south, the Reserve Army would attack on the north in conjunction. An attempt woud be made to seize Morval, Les Boeufs, Flers and Gueudecourt, through which lay the nearest avenue to the open country beyond. On their capture, the cavalry, supported by the XIV. and XV. Corps, who would follow up at once in rear, would be pushed through the outposts. With the flank guard of all arms established on the general line Morval-Le Transloy, the cavalry would seize the high ground east of the Péronne road, and establish a line in country later to become familiar to the New Zealanders, from Rocquigny through Villers-au-Flos and Riencourt-les-Bapaume to Bapaume itself. They would moreover assist in rolling up the enemy's lines to the north-west by operating against his flank and rear in conjunction with the attack which would be continued against his front."
In the forthcoming battle the Corps objectives were 4 in number, marked in accordance with custom in different tints on the maps and referred to by these colours; firstly the seizure of the Switch Trench with the intermediate defences on the crest (the Green Line); secondly the establishment of a Brown Line in German trenches on the far slopes; thirdly the passage of the Flers System, the capture of Flers village and the consolidation of a Blue Line in front of it; and lastly the carrying of Gueudecourt and establishment of a protective Red Line beyond it, bending back to the north-west to the junction with the NI. Corps, whose advance would soon leave the XV. Corps in a marked salient. Flers fell within the zone of the 4lst Division, in the centre of the Corps, and Gueudecourt within that of the 14th Divisioin, on the right. In addition to minor trench elements the advance would involve the capture of 3 formidable trench systems the Switch, the Flers Line, and the Gird Line that protected Gueudecourt. Opposite the New Zealand sector the German positions were held by Bavarians.
The hour of attack had been fixed for 6.20 a.m. on the 15th of September. Before midnight the troops were all in position. Each man was in light fighting order. Two gas helmets were slung over his shoulders. Over 200 rounds of ammunition were contained in his pouches and bandoliers. In his pocket he carried 2 bombs, and behind on his belt were tied the precious sandbags for consolidation. His greatcoat was left with his pack in the regimental dump, but he retained his waterproof sheet with cardigan jacket rolled inside His waterbottle was filled, and in his haversack was a day's rations and "iron" ration. Fastened down the centre of every other man's back was a shovel or pick. Each platoon carried so many smoke bombs for rendering enemy dugouts untenable and so many flares for signalling to our contact aeroplanes that, marked by white streamers and at black band under the left plane, would hover over them at prearranged hours on the following day and after dawn on the 16th.
By 6 a.m. they had breakfasted, and drunk their rum. A ghostly pallor was now creeping into the sky, and the Otago left could just faintly discern the silhouettes of the gaunt trees in High Wood, whose silence was unbroken by German shells. The watch hand crept slowly and as it were reluctantly toward the appointed time. The weather held out every hope of a fine day. To the second our guns broke out into thunderous uproar, and to the second the leading infantry waves of Auckland and Otago, with bayonets fixed and rifles sloped, clambered out of their assembly trenches and advanced straight up over the hummocks and between the shellholes. The 8 companies moved abreast in 4 waves about 50 yards behind each other. Each wave was made up of 8 platoons in single rank, some 3 yards separating man from man. The advance was marked by admirable direction pace and alignment. To those watching in the Carlton System the long line of sombre figures was visible for a few moments ton obscured by thick clouds of smoke and dust. Trudging up the hill, the men hugged the barrage which lifted 50 yards a minute. They twice knelt down in the shellholes to let it precede, firing as they knelt at the machine guns in Crest Trench. An advanced outpost line called Coffee Trench, which lay in front of the Aucklanders, was crowed in their stride. On reaching Crest Trench more Germans were found than had been expected. On the left in front of Otago some 200 turned and ran over the open for the Switch. Many of them never reached it, for our Lewis Gun teams, waiting for the barrage to lift, raked the fugitives with fire.