Why couldnt the Germans just shoot into the Barrage as it came closer to hit the Entente forces behind it?
An effective Creeping Barrage was usually partnered with a significant amount of counter-battery fire in order to suppress or neutralise enemy artillery batteries.
By the time the creeping barrage became sophisticated and practiced enough to be used reliably (around the third quarter of 1916 during the Somme Offensive), it was being recognised that counter-battery operations were critical if an attack was going to be successful. This meant more heavy guns and more sophisticated methods of detection and location of enemy batteries. On the first day of the Somme, too few heavy guns were allocated to neutralising the German artillery. Of the 1,500 British guns supplied to General Henry Rawlinson for the Somme Offensive, only 133 were truly heavy guns (according to Rawlinson's artillery advisor General Budworth). The Germans had around 476 guns on the Somme front and the british only allocated 180 or so heavy guns to neutralising them and a number of these were shifted to wire cutting operations prior to the attack anyway.
The shift of these guns away from counter-battery duties displays an incredible misunderstanding of the importance of removing enemy guns from the equation. Two years had already demonstrated to both the British and the French that artillery could and would wreak havoc amongst attacking formations of troops. The lack of guns dedicated to counter-battery operations is evidence that these lessons, at least amongst the British, went unheeded. The number of shells allotted to the counter-battery guns is further evidence. Prior and Wilson state that on the second day of the preparatory bombardment, the counter-battery guns only fired 250 shells despite the knowledge that it took German guns on average 500 shells to destroy just a single British battery. The inability of the Royal Artillery to find, identify and subsequently destroy German batteries has been identified as a leading factor behind the catastrophic loss of life suffered by the British on 1 July 1916.
At the southern end of the British line, a different story was being told. This section of line was held by the British XIII Corps and its 1 July objective was the German held village of Montaubaun. It was also here that the British line met the French. The plan for this sector was for XIII Corps, commanded by Lieutenant General Walter Congreve VC, to capture the village and establish a defensive flank at the southern portion of the line. XIII Corps was comprised of the 18th and 30th infantry divisions. Both divisions are significant in that they were comprised entirely of volunteers, rather than regular army soldiers, for whom the Somme would be their first major action. The XIII Corps' performance on 1 July is also notable for the use of a Creeping Barrage. Although there is no definitive proof that XIII Corps employed a creeping barrage on 1 July, there is considerable supporting evidence that such a barrage was implemented. XIII Corps’ orders state that “the field artillery barrage will creep back by short lifts … the infantry will follow close behind the barrage as safety admits.” Regardless of whether XIII Corps knowingly utilised what would become known as the creeping barrage
The commander of the 18th Division, General Ivor Maxse, requested that the planned barrage start immediately in front of the trenches occupied by his division. This request was denied on the grounds that it would endanger his troops. In order to mitigate the distance his infantry would have to cross in order to catch up with the barrage, Maxse changed the 18th Division’s jumping off point from a position in No Man’s Land. By doing so, the infantry were able to catch up to their protective barrage rapidly and to occupy the German trenches before the German infantry were capable of responding. The 18th and 30th Divisions would prove to be the most successful British units on 1 July, with the 30th Divisions achieving the greatest advance of the day after capturing the German front line within minutes of reaching it. Such was their success that the infantry following the creeping barrage had to wait for the barrage to lift before they could resume their advance. This was in stark contrast to formations in other sectors that used a form of creeping barrage that often found the infantry struggling to keep up with the rapid advance of the barrage. While XIII Corps was not the only British formation to provide a form of the creeping barrage on 1 July, it did provide the most accurate and the best timed of the variations deployed along the Somme Front. Prior and Wilson have stated that it was this combination, coupled with unconventional tactics such as Ivor Maxse’s advanced jumping off position, that successfully suppressed the German defences and allowed the XIII Corps infantry brigades to achieve their objectives swiftly and successfully.
The success of the XIII Corps was not all of their own making, however. The French XX Corps held the line directly to the right of the British and were fearful of the effect German artillery positioned in the Montauban sector could have on their own attacking infantry. For this reason, XX Corps committed a portion of their heavy guns to counter-battery operations. Coupled with XIII Corps’ rather unusual prioritisation of counter-battery work, the vast majority of German artillery batteries facing these formations were neutralised. Such was the success of this counter-battery work that after achieving all their objectives, the 18th Division, while consolidating their position, found they faced fire from only a single German artillery gun.
As the war progressed, the creeping barrage and counter-battery operations only became more sophisticated. At Vimy Ridge the following year, German artillery was almost completely silenced prior to the commencement of the Canadian attack and the Creeping Barrage was provided by 1,400 field guns that forced the Germans to remain in their bunkers and dugouts until the Canadian infantry was already on top of them. With such a heavy bombardment, there was no possibility of German defenders firing through the approaching barrage to hit the infantry or for German artillery to respond.
Sources:
British Fighting Methods in the Great War by Paddy Griffith
Fire-Power: The British Army Weapons & Theories of War 1904-1945 by Shelford Bidwell and Dominick Graham
The Evolution of Weapons and Warfare by Trevor N Dupuy
Battle Tactics of the Western Front: The British Army's Art of Attack, 1916-1918 by Paddy Griffith