Large numbers of posts for machine-guns to fire an overhead barrage were built and protective pits were dug for mules, each of which was to carry rounds of ammunition to advanced troops. (Machine-guns were fired like artillery, over the heads of the advancing infantry. The bullets of an overhead barrage came down ahead of the attacking troops on German-held areas, forcing the garrison under cover.) Three field companies of engineers with a pioneer battalion were kept in reserve, to follow up the attacking infantry, rebuild roads and work on defensive positions as ground was consolidated. The divisional artillery devised a creeping and standing barrage plan and time-table, tailored to the estimated rates of advance of the infantry. The standing barrage lifts were to keep all trenches within of the infantry under continuous fire. The howitzer, howitzer and howitzers involved, were to change targets only when infantry got within . The 18-pounder field gun standing barrages would then jump over the creeping barrages to the next series of objectives. The concealed guns of the Guards Division field artillery were to join the creeping barrage for the advance at and at the 112th Army Field Brigade was to advance to the old front line, to be ready for an anticipated German counter-attack by .