of mobile warfare, and from the experience GHQ emphasised the need to get all light weaponry as far forward as possible to support infantry, and that "Covering fire of 18-pounders and 4.5-inch howitzers can not be too far exploited" [i.e. should be exploited as much as possible]. It also warned "There was tendency, due to trench warfare, among C.R.A.s to attempt to control individual batteries. Brigade or group commanders should be given a task and allowed to carry it out". At the opening of the Battle of Arras on 9 April 1917, the order was for 18-pounders to fire 50% HE and 50% shrapnel in the creeping barrage ahead of the advancing infantry, with one gun for every 20 yards of front. While a few commanders varied this slightly, such as Brigadier-General Tudor, CRA of 9th (Scottish) Division, who chose 75% HE and 25% smoke, the opening was notable for the first use of a coordinated fireplan across the whole front of several armies, with a common strategy linking infantry with artillery and coordinating the advance of various types of artillery. For instance, the 18-pounders were to move forward when the infantry reached their Phase 2 objective and the 60-pounders and 6-inch howitzers would move forward to take their vacated firing positions. This contrasted with the Somme, where individual Corps and Division commanders used their own fire plans and assault tactics. For the Third Battle of Ypres in July 1917, the plan was for wire cutting to be done by mortars and howitzers, "to conceal the strength of the field guns". 1,098 18-pounders, one for every 15 yards on average, would include shrapnel in firing a creeping barrage starting close to the British trenches and moving forward at 100 yards in 4 minutes. Field batteries were to advance beyond no-mans land as the priority was to protect the infantry while they were "consolidating on their objectives" (i.e. gaining and holding new advanced positions). In the opening barrage for the first phase on 31 July, the Battle of Pilckem Ridge, 2/3s of the 18-pounders fired in the creeping barrage at four rounds per minute and 1/3 fired in the standing barrage on the German second line. The barrage was generally successful; but as the weather deteriorated, tracks turned to mud and shell holes filled with water, it became nearly impossible for guns to advance in support of the infantry as planned.