 The Second Army devised a centralised artillery plan of great sophistication , following the practice established at the Battle of Arras in April 1917 . The use of field survey , gun calibration , weather data and a new and highly accurate 1 : 10 @,@ 000 scale map , gave British artillery much improved accuracy . Target @-@ finding became systematic , with the use of new sound @-@ ranging equipment , better organisation of flash @-@ spotting and the communication of results through the Army Report Centre at Locre Château . Second Army counter @-@ battery artillery bombardments increased from twelve in the week ending 19 April , to 438 in the last ten days before the attack . A survey of captured ground after the battle found that 90 percent of the German artillery positions had been plotted . The 2nd Field Survey Company also assisted the mining companies by establishing the positions of objectives within the German lines , using intersection and a special series of aerial photographs . The company surveyed advanced artillery positions , so that guns moving forward to them once the battle had begun could begin firing as soon as they arrived at the positions . 
