 Complete the following phrase:  The British had substantially increased the amount of artillery on the Western Front after the Battle of Loos in late 1915 but the length of front to be bombarded on the Somme led to the preparatory bombardment being planned to last for five days. There had been a debate about the merits of a short hurricane bombardment but there were insufficient guns quickly to destroy German field defences and be certain that barbed wire was cut, given the dependence of the artillery on air observation and the uncertain weather. The artillery had to cut barbed wire and neutralise German artillery with counter-battery fire. The British artillery fired more than shells during the preliminary bombardment, more than in the first year of the war. On 1 July, another were fired; the guns could be heard on Hampstead Heath, away. While this weight of bombardment was new for the British, it was common on the Western Front; at the 