On the morning of 1 July 1916, the first day of the Battle of the Somme during World War I, underground explosive charges planted by British tunnelling units were detonated beneath the German front lines. The joint explosion of these mines ranks among the largest artificial non-nuclear explosions.
Eight big and eleven tiny charges were buried deep in the chalky earth to make up the 19 mines. They were "overcharged" to throw up high lips for screening and to give advantage to the attackers if they were able to capture the resulting craters. The larger mines were located near Beaumont-Hamel beneath Hawthorn Ridge Redoubt and near La Boisselle (Lochnagar, Y Sap, and Glory Hole charges), Fricourt (Triple Tambour mines), Bulgar Point and Kasino Point. The smaller charges for removing German positions, such as machine gun posts, were laid from the ends of comparatively shallow tunnels.
In addition to the mines, the British tunnelling units also prepared a series of shallow saps extending from the British positions into the no man's land. They allowed the infantry to attack the Germans from a comparatively short distance once the battle commenced.
When they were fired, the Lochnagar and Hawthorn Ridge mines were the largest ever detonated, and reports suggest that their sound could be heard in London and beyond. The mine detonations on the first day of the Somme were surpassed by those fired at the start of the Battle of Messines the following year.
Background
1914
French and German military operations began on the Somme in September 1914. After the German advance towards Albert had been brought to a halt at La Boisselle and attempts to resume offensive warfare in October had not been successful, both sides reduced their attacks to local operations or raids and began to fortify their remaining positions with underground works. On 18 December, the French captured La Boisselle's village cemetery at the west end of a German salient and established an advanced post only from the German front line. By 24 December, the French forced the Germans back from the cemetery and the western area of La Boisselle but their advance was stopped a short distance forward at L'îlot de La Boisselle, in front of German trenches protected by barbed wire. Once the location of a farm and a small number of buildings, became known as Granathof (German: "shell farm") to the Germans and later as Glory Hole to the British. On Christmas Day 1914, French engineers sank a first mine shaft at La Boisselle. Local but heavy fighting underground also took place in the winter of 1914 and spring of 1915 at Fricourt, Bois Français and Carnoy.
1915
From January 1915 to the start of the Battle of the Somme in July 1916, L'îlot de La Boisselle was the scene of fierce underground fighting. Having started mining at La Boisselle shortly after the French, the Bavarian Engineer Regiment 1 continued digging eight galleries towards . On 5 January, French sappers were heard digging near a gallery and a camouflet was quickly placed in the gallery and blown, collapsing the French digging and two German galleries in the vicinity. A charge was blown on 12 January, which killed more than forty French soldiers. On the night of three more German mines were sprung close to . On the night of a German sapper at La Boisselle inadvertently broke into French gallery, which was found to have been charged with explosives; a group of volunteers took racking minutes to dismantle the charge and cut the firing cables. Between April 1915 and January 1916 alone, sixty-one mines were sprung around , some with of explosives.