The charge at Lochnagar was one of 19 mines that were dug under the German lines on the British section of the Somme front, to assist the infantry advance at the start of the battle.

A German advance westwards towards Albert was stopped by the French at La Boisselle and attempts to resume offensive warfare in October failed.

[2] Fighting continued in no man's land at the west end of La Boisselle, where the opposing lines were 200 yd (180 m) apart, even during lulls along the rest of the Somme front.

[4] On 24 July, 174th Tunnelling Company established headquarters at Bray, taking over some 66 shafts at Carnoy, Fricourt, Maricourt and La Boisselle.

[9] The Germans in La Boisselle had fortified the cellars of the ruined houses and cratered ground in the vicinity made a direct infantry assault on the village impossible.

Y Sap and Lochnagar mines, named after the trenches from which they were dug, were excavated 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.

Two officers and sixteen 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 100 ft (30 m).

After the Black Watch had arrived at La Boisselle at the end of July 1915, many fortifications, originally dug by the French, had been given Scottish names.

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 15 ft (4.6 m) high rim and bury nearby trenches.

[11] An officer wrote 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.

German artillery also began to bombard the crater, where wounded and stragglers sought shelter, particularly those from Sausage Valley to the south of the village.

British artillery began to fire on the crater, which led to shell bursts on both slopes, leaving the men inside with nowhere to hide.

[16] The blowing of the Y Sap and Lochnagar mines was witnessed by pilots who were flying over the battlefield to report back on British troop movements.

2nd Lieutenant Cecil Lewis (3 Squadron) was warned against flying too close to La Boisselle during his patrol, where two mines were due to go up but watched from a safe distance.

The barrage had lifted to the second-line trenches, the infantry were over the top, the attack had begun.As aircraft from 3 Squadron flew over the III Corps area, observers reported that the 34th Division had reached Peake Wood on the right flank, increasing the size of the salient which had been driven into the German lines north of Fricourt but that the villages of La Boisselle and Ovillers had not fallen.

On 3 July, air observers noted flares lit in the village during the evening, which were used to plot the positions reached by British infantry.

The ruined village was meant to be captured in 20 minutes but by the end of the first day on the Somme, the III Corps divisions had suffered more than 11,000 casualties for no result.

[6] William Orpen, an official war artist, saw the mine crater in 1916 while touring the Somme battlefield, collecting subjects for paintings and described a wilderness of chalk dotted with shrapnel.

[25] The site attracts about 200,000 visitors a year and there is an annual memorial service on 1 July, to commemorate the detonation of the mine and the British, French and German war dead, when poppy petals are scattered into the crater.