In its February 1917 Technical Notes on 18-pounder Barrages, GHQ stated shrapnel and HE barrages would normally cover to a depth of 200 yards and expressed its preference for timed shrapnel (T.S.) for creeping barrages, due partly to shrapnel directing its force forward hence being safer for those following, especially if it fell short. 50% air bursts and 50% percussion (bursting on contact) was considered optimal except on "very bad ground" where percussion rounds would mostly be wasted. HE with its lateral bursting was considered more dangerous to advancing troops (as they were assumed to be in a line abreast) than shrapnel if it burst short, but lateral bursts were considered to have less effect on the enemy as they had less "forward effect". HE with delay was difficult for advancing troops to stay close behind, as it burst 30–40 yards beyond the point of initial contact. HE without delay was assessed as effective only if it burst actually in the enemy trench. With a proper barrage program and fuze setting, timed shrapnel creeping barrage was considered optimal. British regular army field gunners were already proficient in accurately timed low shrapnel bursts in 1914, as demonstrated in the early battles, but few remained by early 1917 and many gunners were relatively new recruits and inexperienced; HE had only been in use with 18-pounders for two years, so this note perhaps reflects a desire to stick with a proven method for which they could still draw on a nucleus of experts. Shrapnel appears to have been favoured for creeping barrages and a mix of shrapnel and HE for standing barrages and other tasks.