General Ferdinand Foch , commander of `` groupe des armées du nord '' ( Northern Army Group ) and co-ordinator of the armies on the Somme , was unable to continue the sequential attacks Attack by the Anglo-French armies achieved Achieve in September , because persistent rain , mist and fog grounded aircraft , turned Change the battlefield Hostile_encounter into a swamp and greatly increased Cause_change_of_position_on_a_scale the difficulty of transporting Military_operation supplies Supply to the front over the few roads in the area and the land that had been devastated Destroying since 1 July .