 German artillery positions and the second ( Höhen ) line were not visible to British ground observers . For observation over the rear slopes of the ridge , 300 aircraft were concentrated in II Brigade RFC and eight balloons of II Kite Balloon Wing were placed 3 @,@ 000 – 5 @,@ 000 feet ( 910 – 1 @,@ 520 m ) behind the British front line . The Second Army artillery commander , Major @-@ General George Franks , co @-@ ordinated the corps artillery plans , particularly the heavy artillery arrangements to suppress German artillery , which were devised by the corps and divisional artillery commanders . The Second Army Report Centre at Locre Château was linked by buried cable to each corps report centre , corps heavy artillery headquarters , divisional artillery headquarters , RFC squadrons , balloon headquarters , survey stations and wireless stations . Responsibility for counter @-@ battery fire was given to a counter @-@ battery staff officer with a small staff , who concentrated exclusively on the defeat of the German artillery . A conference was held each evening by the counter @-@ battery staffs of divisions and corps , methodically to collate the day 's reports from observation aircraft and balloons , field survey companies , sound ranging sections and forward observation officers . Each corps had a counter @-@ battery area , which was divided into zones and allotted to heavy artillery groups . Each heavy artillery group headquarters divided their zones into map squares , which were allotted to artillery batteries , required to be ready swiftly to open fire on them . 
