[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.

[6] 1st Canadian Tunnelling Company was formed in eastern Canada, then moved to France and into the Ypres Salient for instruction in early 1916.

[1] From spring 1916 onwards, the Germans drove long galleries beneath The Bluff, and on 25 July 1916 the 1st Company of the 24th Pioneers blew a mine under the ridge.

The 1st Canadian Tunnelling Company had, however, anticipated the blow so casualties were minimized[7] and the attacking German infantry did not capture the ridge.

The tunnelling by machine in the Belgian blue clay was problematic and the War Diary lists numerous stoppages for repairs.