French Second Army at the end of July 1915. Miners brought from Germany late in 1914 tunnelled under Beaumont-Hamel and the vicinity to excavate shelters in which infantry companies could shelter and against which even heavy artillery could cause little damage. On the Somme front, a construction plan of January 1915, by which Falkenhayn intended to provide the western armies with a means to economise on infantry, had been completed. Barbed-wire obstacles had been enlarged from one belt wide to two belts wide and about apart. The front line had been increased from one trench to three, apart, the first trench () to be occupied by sentry groups, the second () to accommodate the front-trench garrison and the third trench for local reserves. The trenches were traversed and had sentry-posts in concrete recesses built into the parapet. Dugouts had been deepened from to , apart and large enough for An intermediate line of strong points (the ) about behind the front line had also been built. Communication trenches ran back to the reserve line, renamed the second line, which was as well built and wired as the first line. The second line was built beyond the range of Allied field artillery, to force an attacker to stop and move field artillery forward before assaulting the line. 1915–1916 On New Year's Eve 1915, a small mine was sprung under Redan Ridge north of Beaumont-Hamel, followed by German mine explosions on January. British mines were blown on January 1916 and both sides sprung mines in February; the Germans then dug a defensive gallery parallel to the front line to prevent surprises. On the night of a German raid by II Battalion, Reserve Infantry Regiment 119 (RIR 119) took place near Y Ravine, against the 2nd South Wales Borderers of the 29th Division and caused 112 casualties, for a loss of three killed and one man wounded. A big raid by the British on 30 April was seen by alert defenders and repulsed by small-arms fire and artillery as soon as it began. A report by the local German commander, showed that the preparations for the raid had been noticed a week before the attempt. After the Second Battle of Champagne in 1915, construction of a third line another back from the had been begun in February 1916 and was nearly complete on the Somme front by 1 July. Divisional sectors north of