[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.

[5][7] 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.

[9] As Allied preparations for the Battle of the Somme (1 July – 18 November 1916) were begun, the tunnelling companies were to make two major contributions 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.

[11] Four mines were planned at La Boisselle: Two 3,600-kilogram (8,000 lb) charges (known as No 2 straight and No 5 right) were planted at L'îlot, intended to wreck German tunnels[12] and create crater lips to block enfilade fire along no man's land.

To assist the attack on the village, two further mines, known as Y Sap and Lochnagar after the trenches from which they were dug, were laid to the north-east and the south-east of La Boisselle on either side of the German salient[13][14] – see map.

A month before the handover, eighteen men of the 185th Tunnelling Company (2 officers, 16 sappers) died to a German camouflet at La Boisselle on 4 February 1916.

In the second half of 1916 the British constructed strong defensive underground positions, and from August 1916, the Royal Engineers developed a mining scheme to support a large-scale infantry attack on the Vimy Ridge proposed for autumn 1916, although this was subsequently postponed.

[16] After September 1916, when the Royal Engineers had completed their network of defensive galleries along most of the front line, offensive mining largely ceased[17] although activities continued until 1917.

[1] Prior to the Battle of Vimy Ridge (9 – 12 April 1917), the British tunnelling companies secretly laid a series of explosive charges under German positions in an effort to destroy surface fortifications before the assault.

The gallery had been pushed silently through the clay, avoiding the sandy and chalky layers of the Vimy Ridge, but by 9 April 1917 was still 21 metres (70 ft) short of its target.