The Battle for Longueval and Delville Wood, had started with a charge by the 2nd Indian Cavalry Division between Longueval and High Wood and two weeks after the wood was cleared, tanks went into action for the first time. A number of important tactical lessons were learned from the battle for the village and wood. Night assembly and advances, dawn attacks after short, concentrated artillery barrages for tactical surprise nd building defensive lines on the fringes of wooded areas, to avoid tree roots in preventing digging and to keep clear of shells which were detonated by branches, showering troops with wood splinters. Troops were relieved after two days, as longer periods exhausted them and consumed their ammunition, bombs and rations. The persistence of the British attacks during July and August helped to preserve Franco-British relations, although Joffre criticised the large number of small attacks on 11 August and tried to cajole Haig into agreeing to a big combined attack. On 18 August, a larger British attack by three corps was spoilt by several days of heavy rain, which reduced artillery observation and no ground was gained at Delville Wood.