The German Army evacuates Serre, Miraumont, Petit Miraumont, Pys and (facing the I Anzac Corps) Warlencourt near Bapaume, falling back 25 miles to establish stronger positions along the Hindenburg Line. The shorter defensive position behind the Noyon Salient was built to economise on manpower, contain an Allied breakthrough and make possible a deliberate withdrawal to prepared positions utilising strong-points and protected by thick wire entanglements. By destroying the infrastructure and demolishing civilian buildings in the salient before a withdrawal, the Germans could dislocate Franco-British offensive preparations, by forcing them to advance into a wasteland. The British and French armies would need about eight weeks to rebuild roads, bridges and railways in the abandoned area before they could attack. A shorter Western Front could be held with fewer troops and by incorporating the lessons of defensive battle on the Somme, the importance of troop dispersal, reverse-slope positions, defence in depth and camouflage, German infantry casualties could be reduced. While the German army recuperated from the losses of 1916, protected by the Hindenburg Line and similar defensive positions on the rest of the Western Front, a return to unrestricted submarine warfare and a strategic bombing offensive against Britain were planned.