[2] Following consultations between the Engineer-in-Chief of the BEF, Brigadier George Fowke, and the mining specialist John Norton-Griffiths, the War Office formally approved the tunnelling company scheme on 19 February 1915.

[3] To make the tunnels safer and quicker to deploy, the British Army enlisted experienced coal miners, many outside their nominal recruitment policy.

These companies each comprised 5 officers and 269 sappers; they were aided by additional infantrymen who were temporarily attached to the tunnellers as required, which almost doubled their numbers.

[2] The success of the first tunnelling companies formed under Norton-Griffiths' command led to mining being made a separate branch of the Engineer-in-Chief's office under Major-General S.R.

[4] The formation of twelve new tunnelling companies, between July and October 1915, helped to bring more men into action in other parts of the Western Front.

[1] In the Somme sector of the Western Front, local but very fierce underground fighting had taken place in the winter of 1914 and spring of 1915 at La Boisselle, Fricourt, Bois Français and Carnoy.

With the war on the surface at stalemate, both sides continued to probe beneath the opponent's trenches and detonate ever-greater explosive charges.

[8] In October 1915, 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.

[9] On 19 November 1915, 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 2,700 kilograms (6,000 lb) of explosive.

The tunnelling companies were to make two major contributions to the Allied preparations by placing 19 large and small mines beneath the German positions along the front line and by preparing a series of shallow Russian saps from the British front line into no man's land, which would be opened at zero hour and allow the infantry to attack the German positions from a comparatively short distance.

In the front section allocated to the 36th (Ulster) Division, ten saps were run from the British lines into no-man's land north-east of Thiepval Wood.

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[9][8] – see map.

[8] A month before the handover, 18 men of the 185th Tunnelling Company (2 officers, 16 sappers) were killed on 4 February when the Germans detonated a camouflet near the British three-level mine system, starting from Inch Street, La Boisselle, the deepest level being just above the water table at around 30 metres (100 ft).

After the Black Watch had arrived at La Boissselle at the end of July 1915, many existing Allied fortifications, originally dug by the French, had been given Scotland-related names.

The Lochnagar mine probably had the first deep incline shaft, which sloped 1:2–1:3 to a depth of about 29 metres (95 ft) – see map Archived 26 June 2015 at the Wayback Machine.

Flints were carefully prised out of the chalk and laid on the floor; if the bayonet was manipulated two-handed, an assistant caught the dislodged material.

Spoil was placed in sandbags and passed hand-by-hand, along a row of miners sitting on the floor and stored along the side of the tunnel, later to be used to tamp the charge.

The tunnels did not quite reach the German front line but the blast would dislodge enough material to form a 4.6 metres (15 ft) high rim and bury nearby trenches.

[14] Captain Stanley Bullock described the conditions of the work: At one place in particular our men swore they thought he [the German enemy] was coming through, so we stopped driving forward and commenced to chamber in double shifts.

Half an hour, sometimes once sometimes three times a day, in deadly silence with the geophone to your ears, wondering whether the sound you heard was the Boche working silently or your own heart beating.

The explosion of the Lochnagar mine was initiated by Captain James Young of the 179th Tunnelling Company, who pressed the switches and observed that the firing had been successful.

Sections of 179th Tunnelling Co assisted the field companies of 42nd (EaL) Divisional Engineers in digging deep dugouts in the Hébuterne sector.