The final Entente offensive of the spring was the Second Battle of Artois, an offensive to capture Vimy Ridge and advance into the Douai plain. The French Tenth Army attacked on 9 May after a six-day bombardment and advanced to capture Vimy Ridge. German reinforcements counter-attacked and pushed the French back towards their starting points because French reserves had been held back and the success of the attack had come as a surprise. By 15 May the advance had been stopped, although the fighting continued until 18 June. In May the German Army captured a French document at La Ville-aux-Bois describing a new system of defence. Rather than relying on a heavily fortified front line, the defence was to be arranged in a series of echelons. The front line would be a thinly manned series of outposts, reinforced by a series of strongpoints and a sheltered reserve. If a slope was available, troops were deployed along the rear side for protection. The defence became fully integrated with command of artillery at the divisional level. Members of the German high command viewed this new scheme with some favour and it later became the basis of an elastic defence in depth doctrine against Entente attacks.