 The artillery duel went on for several weeks before the attack, with British batteries taking heavy casualties from German CB fire and gas shelling.The offensive opened on 31 July with the Battle of Pilckem Ridge, the infantry advancing behind the biggest barrage programme yet devised.Despite setbacks – II Corps suffering the worst hold-up in front of Westhoek on the Gheluveldt Plateau and losing the barrage – a general advance of was achieved, but by evening rain was falling heavily and it proved almost impossible to move the guns and ammunition up through the mud.