The Germans were able to nullify much of the Anglo-French material superiority in the battle, particularly during the periods of cold and wet weather in late July and late August. The defence was as piecemeal as British attacks but with the French exposed to converging artillery-fire, on the Flaucourt Plateau south of the Somme and the British bogged down on Bazentin Ridge, the Germans used observation posts around Guillemont and High Wood, to observe fire into the salients around Maurepas and Guillemont from three sides. Poor weather was less of a handicap to the Germans, while they held such commanding ground. Positions were linked with more support and reserve trenches, behind the second position south and east of Delville Wood and new "switch trenches" dug oblique to forward lines, were used to prevent Anglo-French infantry from "rolling up" German defences, from an isolated penetration.