[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.

[4] 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.

[5] 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] The Bluff, located halfway in between Voormezele and Hollebeke, is an artificial ridge in the landscape created by spoil from failed attempts to dig a canal.

[14] Johnston left 172nd Tunnelling Company in early May, when he was succeeded as officer commanding by William Clay Hepburn, a Territorial Army Captain in the Monmouthshire Regiment.

[18] The geology of the Ypres Salient featured a characteristic layer of sandy clay, which put very heavy pressures of water and wet sand on the underground works and made deep mining extremely difficult.

On 21 January 1916, German miners blew several large charges at The Bluff, which caused 172nd Tunnelling Company to halt its work on the shallow galleries in St Eloi in order to complete the deep mines as soon as possible.

[21] When the mines were fired at 4.15 a.m. on 27 March 1916, D1 and D2 were detonated first, followed by H1 and H4, then I and finally F. To witnesses it "appeared as if a long village was being lifted through flames into the air" and "there was an earth shake but no roar of explosion".

[22] The detonation obliterated The Mound and killed or buried some 300 men of the 18th Reserve Jäger Battalion;[23] two miles away, at Hill 60, the trenches rocked and heaved.

[22] The Royal Northumberland Fusiliers attacked and held the D1, D2 and F craters, but efforts to dig communications trenches to their positions failed under the heavy German fire, the muddy ground and debris thrown up by the explosions.

From spring 1916, the British had deployed five tunnelling companies along the Vimy Ridge, and during the first two months of their tenure in the area, 70 mines were fired, mostly by the Germans.

[27] As part of this process, the New Zealand Tunnelling Company took over a sector between Roclincourt and Écurie from the French 7/1 compagnie d'ingénieurs territoriaux during March 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.

[18] After September 1916, when the Royal Engineers had completed their network of defensive galleries along most of the front line, offensive mining largely ceased[27] although activities continued until 1917.

[18] Prior to the Battle of Vimy Ridge, 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.

The brick plinth bears transparent plaques with details of the mining activities by 172nd Tunnelling Company and an extract from the poem Trenches: St Eloi by the war poet T.E.