of miners sitting on the floor and stored along the side of the tunnel, later to be used to tamp the charge. When about from the , the tunnel was branched and the end of each branch was enlarged to form a chamber for the explosives, the chambers being about apart and deep. When finished, the access tunnel for the Lochnagar mine was and had been excavated at a rate of about per day, until about long, with the galleries ending beneath the . The mine was loaded with of ammonal in two charges of and . As the chambers were not big enough to hold all the explosive, the tunnels that branched to form the 'Y' were also filled with ammonal. One branch was long and the other long. The tunnels did not quite reach the German front line but the blast would dislodge enough material to form a high rim and bury nearby trenches. The Lochnagar and the Y Sap mines were "overcharged" to ensure that large rims were formed from the disturbed ground. Communication tunnels were also dug for use immediately after the first attack, including a tunnel across no man's land to a point close to the Lochnagar mine, ready to extend to the crater after the detonation as a covered route. The mines were laid without interference by German miners but as the explosives were placed, German miners could be heard below Lochnagar and above the Y Sap mine. An officer wrote Battle 1 July The four mines at La Boisselle were detonated at on 1 July 1916, the first day on the Somme. 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. The two charges of the Lochnagar mine created a smooth-sided, flat-bottomed crater in diameter excluding the lip and across the full extent of the lip. It had obliterated between of the German dug-outs, all said to have been full of German troops. The Lochnagar mine, along with Y Sap mine, was the largest mine ever detonated. The sound of the blast was considered the loudest man-made noise in history up to that point, with reports suggesting it was heard in London. They would be surpassed a year later by the mines in the Battle of Messines. The Lochnagar mine lay on the