a successful offensive, while the French believed they needed 1:1. General Farndale justified the retention of 2:1 field artillery as "Field guns were essential to attack targets close to our own troops and to play their part in the tactical plan". During 1915, 18-pounder ammunition production was equally divided between HE and shrapnel, but expenditure was mostly shrapnel, 88% in September and November. 1916 Field artillery (both 18-pounder and 4.5-inch howitzer) was used successfully during the pre-Zero fire in the Battle of the Somme in late June – early July 1916, when the British heavy artillery damaged German defensive works and forced troops into the open to rebuild them they were successfully fired on with shrapnel. The use of field guns to provide a covering fire barrage that neutralized the enemy during the infantry advance was used and improved during the Battle of the Somme, forcing the enemy to remain in shelters while the infantry advanced immediately behind the bursting shells – "... It is therefore of the first importance that in all cases the infantry must advance right under the field artillery barrage, which must not uncover the first objective until the infantry is within 50 yards of it". The small bursting range of the shell was an advantage in this case, as advancing troops could approach close to it. The 18-pounder's role was spelled out following the Somme battles "... primarily in barrage fire, repelling attacks in the open, raking communications, wire cutting and sometimes for neutralising guns within their reach, destroying breast-works and barriers with HE and preventing repair work on defenses beyond the reach of infantry weapons". 18-pounder ammunition requirements were predominantly shrapnel during 1916, although in the latter part of the year it shifted back to equality between HE and shrapnel. In July 1916, standard contract prices for UK produced shells were 12 shillings and 6 pence (62.5 pence in modern terms) for HE and 18 shillings and 6 pence for shrapnel. US and Canadian prices were significantly higher. The lowest price achieved for 18-pounder HE shells was 8 shillings and 11 pence (44.8 pence) later in 1916. 1917 The January 1917 "Artillery in Offensive Operations" estimated that 18-pounders needed 7.5 shrapnel rounds + 5% HE per yard of front at medium range to cut barbed wire defences, and 20 rounds of HE to destroy trenches in enfilade. The destruction of trenches frontally was generally