The barrage was highly complicated, as, owing to the configuration of the German salient and the varying rate of the advance, it lifted off none of the objectives at the same moment all along the line. Meticulous care was taken by Army Headquarters to ensure that the preparation was as complete as human forethought could make it. Each morning air photographs, showing the effect of the previous day's bombardment, were circulated to Divisions in the line. Each Division was required to state, day by day, what further special bombardment it desired. From its observation post on Kemmel Hill the Staff of the 36th Division could see practically all the slope of the Messines Ridge, from just above the dip of the Steenebeek valley to the crest. Day by day it studied the ground during the bombardment. A trench or concrete work which did not appear to have been sufficiently shelled was noted, and request made that it should receive further attention next day. Such requests were invariably met. Trenches and dug-outs were shelled again and again, till Divisional Headquarters declared itself satisfied. Many of the concrete structures were revealed only when the bombardment of the trenches had blown away the earth about them. They were then subjected to the fire of heavy howitzers till destroyed. Finally, each Division was asked to state if it were satisfied with the preparation. In the case of the 36th Division at least, the answer was an enthusiastic affirmative. The sympathy and understanding which existed between the Staff of the Second Army and the man in the fighting line created a moral tone of incalculable value to the Army's efficiency as a striking force. The work of the preliminary bombardment threw a great strain upon the personnel of the artillery, though such rest as possible was given by carefully organized reliefs. The infantry was greatly impressed with the results it could witness. In particular the liaison between infantry and heavy gunners, hardly thought of before this action, was of the closest, the artillery officers bringing battalion commanders aeroplane photographs to show the results of the bombardment on their front.