Both sides had many casualties and chronic communication problems; inclement weather grounded aircraft, obscured the view and slowed movement on the roads, which had been severely bombarded and turned to mud as soon as it rained. Trenches and shell holes filled with water, which made infantry movement exceedingly difficult and exhausted trench garrisons. The British and French found it impossible to arrange co-ordinated attacks and fought many small piecemeal actions, rather than general attacks until 15 September. British-French co-operation broke down again and the French did not attack on 15 September, when the British captured the wood during the Battle of Flers–Courcelette (15–22 September). The German defenders had great difficulty finding fresh troops for the Somme front, despite ending the Battle of Verdun and had to send divisions to the Eastern Front and to Romania after it declared war on 27 August. Turnover of German divisions was high and many had to be withdrawn and replaced after fourteen days in the front line. The Germans lacked the resources to make many big organised counter-attacks and those at High Wood and the vicinity were often as costly and ineffective as corresponding British attacks.