In September 1915 the Entente allies launched another offensive, with the French Third Battle of Artois, Second Battle of Champagne and the British at Loos. The French had spent the summer preparing for this action, with the British assuming control of more of the front to release French troops for the attack. The bombardment, which had been carefully targeted by means of aerial photography, began on 22 September. The main French assault was launched on 25 September and, at first, made good progress in spite of surviving wire entanglements and machine gun posts. Rather than retreating, the Germans adopted a new defence-in-depth scheme that consisted of a series of defensive zones and positions with a depth of up to .