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 small 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.
In summer 1915, the French mine workings in the La Boisselle area were taken over by the Royal Engineers as the British moved into the Somme front. Great secrecy was maintained to prevent the discovery of the mines as no continuous front line trench ran through L'îlot de La Boisselle, which was defended by posts near the mine shafts. G. F. Fowke moved the 174th and 183rd Tunnelling Companies into the area, but at first the British did not have enough miners to take over the large number of French shafts; the problem was temporarily solved when the French agreed to leave their engineers at work for several weeks. On 24 July, 174th Tunnelling Company established headquarters at Bray, taking over some 66 shafts at Carnoy, Fricourt, Maricourt and La Boisselle. No man's land just south-west of La Boisselle was very narrow, at one point about wide, and had become pockmarked by many chalk craters. The Germans had also dug defensive transverse tunnels about long, parallel to the front line. To provide the men needed for significant counter-mining operations against the Germans, the British formed the 178th and 179th Tunnelling Companies in August, followed by the 185th and 252nd Tunnelling Companies in October. The 181st Tunnelling Company was also present on the Somme.
The British tunnelling companies dramatically increased the scale of mining operations by extending and deepening the system, first to and ultimately . In August, the French and Germans had been working at a depth of ; the size of their charges had reached . The underground war continued with offensive mining to destroy the opponents' strong points and defensive mining to destroy tunnels, which were long. In addition to their offensive and defensive works, the Royal Engineers also dug deep wells to supply the troops with drinking water. In October, the 179th Tunnelling Company began to sink a series of deep shafts in an attempt to forestall German miners who were approaching beneath the British front line. At W Shaft they went down from to and began to drive two counter-mine tunnels towards the Germans. From the right-hand gallery the sounds of German digging grew steadily louder. On 19 November, 179th Tunnelling Company's commander, Captain Henry Hance, estimated that the Germans were 15 yards away and ordered the mine chamber to be loaded with of explosive. This was completed by midnight from 20 to 21 November. At 1.30 am on 22 November, the Germans blew their charge, filling the remaining British tunnels with carbon monoxide. Both the right and left tunnels were collapsed, and it was later found that the German blow had detonated the British charge. The wrecked tunnels were gradually re-opened, but about thirty bodies still lie in the tunnels beneath La Boisselle.
Prelude As part of the Allied preparations for the Battle of the Somme, the British intensified their underground operations in several selected front line sectors. This was particularly the case of the many Russian saps prepared in the various sectors from February 1916. The Royal Engineer mining units involved in preparing the battle were the 174th, 178th, 179th, 181st, 183rd, 185th and 252nd Tunnelling companies.
VII Corps In the northernmost sector of the British front line, which was allocated to VII Corps in front of Gommecourt, no mines were prepared by the Royal Engineers for the offensive on 1 July. The British Army would use the neighbouring villages of Hebuterne and Foncquevillers as bases for the assault on Gommecourt, resulting in a severe defeat for the attacking force.
VIII Corps
In the British front sector allocated to VIII Corps at Beaumont-Hamel, 252nd Tunnelling Company dug a large mine, code named H3, at Hawthorn Ridge Redoubt.The Tunnelling Companies RE access date 25 April 2015 and prepared twelve Russian saps facing Serre. Near the Hawthorn Ridge Redoubt, three tunnels were excavated under no man's land: The first was a tunnel dug overnight to link to the now famous Sunken Lane (shown in the film The Battle of the Somme, released in August 1916) with the old British front line, and through which British units moved into position before the attack. In the early hours of 1 July, the 1st Battalion Lancashire Fusiliers would use this tunnel to move up into the "Sunken Lane", the starting position for their attack on Beaumont-Hamel. The two other tunnels were Russian saps, dug to within of the German front line, ready to be opened at on 1 July, as emplacements for batteries of Stokes mortars. They were called First Avenue and Mary, named after the communications trenches leading into them.
The large H3 mine, located north of First Avenue and Mary, was placed by 252nd Tunnelling Company beneath Hawthorn Ridge Redoubt, the German stronghold on the ridge. Work on H3 began in spring 1916. The tunnellers under the command of Captain Rex Trower dug a gallery for about from the British lines about underground beneath the German position on the crest of the ridge. By the end of May, the mine gallery had been driven , despite considerable trouble caused by the hard chalk and the number of flints in the face. To preserve silence, the face was softened by the application of water. In June the gallery was finished and charged with of ammonal. The VIII Corps commander, Lieutenant-General Aylmer Hunter-Weston, wanted the mine to be sprung four hours before zero hour, so that the crater could be captured and consolidated and the alarm on the German side would have died down. On 15 June, the Fourth Army headquarters ruled that all mines should be blown no earlier than eight minutes before zero but an unsatisfactory compromise was reached with Hunter-Weston to blow the Hawthorn Ridge Redoubt mine ten minutes before zero hour.
X Corps
In the British front sector allocated to X Corps at Thiepval, no mines were prepared by the Royal Engineers for the offensive on 1 July, although they dug a series of Russian saps into no man's land, ready to be opened at Zero Hour and allow the British infantry to attack the German positions from a comparatively short distance. Russian saps in front of Thiepval were the task of 179th Tunnelling Company, which also prepared such saps further south at Ovillers and La Boisselle. In the X Corps front section allocated to the 36th (Ulster) Division, ten Russian saps were run from the British lines into no-man's land north-east of Thiepval Wood. Each of the ten tunnels housed two mortars.
III Corps
In the British front sector allocated to III Corps at La Boisselle, four mines were prepared: Two charges (known as No 2 straight and No 5 right) were planted at at the end of galleries dug from Inch Street Trench by the 179th Tunnelling Company, intended to wreck German tunnels and create crater lips to block enfilade fire along no man's land. As the Germans in La Boisselle had fortified the cellars of ruined houses, and cratered ground made a direct infantry assault on the village impossible, two further mines, known as Y Sap and Lochnagar after the trenches from which they were dug, were laid on the north-east and the south-east of La Boisselle to assist the attack on either side of the German salient in the village – see map.