Meanwhile in the northern zone also, the Australian and New Zealand Army Corps had strengthened their grip on Turkish soil. Whilst in the south we had been attacking and advancing they had been defending and digging themselves more and more firmly into those cliffs on which it had seemed at first that their foothold was so precarious. NO RESPITE FROM SHELLS On May 11, the first time for eighteen days and nights, it was found possible to withdraw the 29th Division from the actual firing line and to replace it by the 29th Indian Infantry Brigade and by the 42nd Division, which had completed its disembarkation two days previously. The withdrawal gave no respite from shells, but at least the men were, most nights, enabled to sleep. The moment lent itself to reflection, and during this breathing space I was able to realize we had now nearly reached the limit of what could be attained by mingling initiative with surprise. The enemy was as much in possession of my numbers and dispositions as I was in possession of their first line of defence; the opposing fortified fronts stretched parallel from sea to straits; there was little scope left now, either at Achi Baba or at Kaba Tepe, for tactics which would fling flesh and blood battalions against lines of unbroken barbed wire. Advances must more and more tend to take the shape of concentrated attacks on small sections of the enemy's line after full artillery preparation. Siege warfare was soon bound to supersede manœuvre battles in the open. Consolidation and fortification of our front, improvement of approaches, selection of machine-gun emplacements and scientific grouping of our artillery under a centralized control must ere long form the tactical basis of our plans. So soon, then, as the troops had enjoyed a day or two of comparative rest I divided my front into four sections. On the left was the 29th Division, to which the 29th Indian Infantry Brigade was attached. In the left centre came the 42nd (East Lancashire) Division, on the right centre stood the Royal Naval Division, and at my right was the Corps Expéditionnaire. Thus I secured organization in depth as well as front, enabling each division to arrange for its own reliefs, supports, and reserves, and giving strength for defence as well as attack. Hitherto the piecemeal arrival of reinforcements had forced a hand-to-mouth procedure upon head-quarters; now the control became more decentralized.