Army) to against French, British and Belgian divisions. The had and field guns, and heavy guns and ten super-heavy howitzers. A reserve of guns and mortars was also being prepared. OHL had divisions in reserve, with the 58th Division and the 115th Division behind the 6th Army. Indications of an attack in Artois had been detected but not signs of a general offensive on the Western Front. The was forced to remain on the defensive, except for limited attacks in Flanders, in the Second Battle of Ypres () and in the Argonne, west of Verdun, until August to cut the main rail line from Paris to Verdun. In memoranda issued on Falkenhayn ordered that the positions of the German armies in France were to be fortified to resist attacks with only small forces, to enable reserves to be sent to Russia. Should part of the front line be lost, it was to be retaken by counter-attack. Behind the line, new defences were to be built and connected by communication trenches, to delay a further attack until reserves could be assembled for a counter-attack. Opposing reinforcements were to be obstructed by a shell-barrage (). On 4 May, Falkenhayn reiterated the need to improve reserve positions and also to build a rear position about behind the front line. During 1915, the German armies on the Western Front increased the front line from one to three trenches, built a second trench system behind the front line and developed the defensive use of machine-guns and artillery, to restrict an attack to a bend () in the line. The Franco-British offensives in 1915 found the German defences in a state of continuous development, the building programme taking time to complete, due to a shortage of labour. Tactical developments In March 1915, Joffre concluded that a period of inactivity would benefit the Germans more than the French; General Ferdinand Foch, commander of the (GPN), proposed an offensive in which a "general action" on the Western Front including the British, to confuse the defenders and pin down reserves, would complement a "decisive action", to break through the German defences at a place where the Germans would not be able to establish a new defensive front by a short retirement. Joffre accepted the proposals on 23 March, with the objective being the seizure of Vimy Ridge and exploitation of the success by an eastwards advance into the Douai