The signal for zero hour was to be the explosion of a mine. In the attack that had been launched against Beaumont Hamel on the first day of the Somme offensive, a mine had been exploded just short of the enemy's front line. As the attack had failed, the enemy had been left in complete possession of this mine. He had fortified it with dug-outs and made considerable use of it both as an observation-post and as a position for snipers. Arrangements had therefore been made to run out another shaft and lay a fresh charge in chambers constructed below this crater. At 5.45 A.M. this mine was successfully exploded, and the artillery opened an intense bombardment of the German position. At this time dawn had only just begun to show signs of breaking. The darkness was further accentuated by a fog, similar to a typical London November fog, which did not lift throughout the day. This fog was a definite asset to the attack, as, though it made the maintenance of direction more difficult, it concealed the movements of the attackers, and prevented the enemy gunners from seeing the artillery signals fired by their infantry. The result was that the hostile artillery barrage on the British front line and in No Man's Land was ragged, and did not open with any intensity until 6.15 A.M. In consequence, the losses from hostile artillery fire in the assembly trenches and while the troops were crossing No Man's Land were negligible. The infantry had crept close to the barrage before it had lifted, so that when it moved forward they succeeded in entering the trench at most points. Indeed, so close did they get to the bursting shells that many of them reported that they were waiting on the outskirts of the remnants of the enemy's entanglements while the barrage was still down in the Boche front line. The 6th Black Watch pressed forward so close to the barrage that they sustained some casualties from it. The two right companies of the 7th Gordon Highlanders took the first line without difficulty. They continued keeping close up to the barrage, each successive wave capturing its objective, until they had occupied the Green line according to the programme. These two companies could not have carried out their task in a more exemplary manner. Throughout this advance on the right flank touch was maintained with the left of a Royal Marine Light Infantry battalion of the 63rd Naval Division. On the rest of the front the attack bore no resemblance to the traditional form of attack as pictured in the illustrated weeklies, or demonstrated by the bayonet-fighting expert. There was no wild charge of Highlanders with flying kilts and glittering bayonets. On the contrary, it was carried out at the rate of an advance of twenty-five yards per minute. As the barrage lifted off a trench, the troops made their way into it as quickly as they could, but a steady double was the most that they could manage. In many cases even that was found impossible.