During the battle of the Somme, the Entente attacked the German Army in order to quicken an allied victory. During the planning stages of the battle the French were supposed to carry out the main attack, with the British in a support role. Because the Germans attacked at Verdun the French were forced to divert reinforcements to that area, so the British had to carry out the main attack. After a first day in which the British failed to achieve most of their objectives and suffered heavy casualties, they slowly began pushing into the German lines. At the end of the battle the Entente penetrated some 10 km into German-occupied territory. The battle is notable for the importance of air power and the first use of the tank. It is also the largest battle of the Great War, with a million men wounded or killed on all sides.