The main gallery of the mine is five hundred and twenty-two feet in length, the side-galleries about forty feet each. My suggestion is that eight magazines be placed in the lateral galleries, two at each end, say a few feet apart, at right angles to the side-gallery, and two more in each of the side-galleries, similarly placed by pairs, situated equidistant from each other, and the end of the galleries: I proposed to put in each of the eight magazines from twelve to fourteen hundred pounds of powder, the magazines to be connected by a trough of powder instead of a fuse.It appears that it was decided that the charge should be eight thousand pounds instead of the larger amount proposed.1 Between four and five o'clock on the morning of July 30th the mine was exploded, and simultaneously the enemy's batteries commenced firing, when, as previously arranged, the column of attack moved forward to the breach, with instructions to rush through it and seize the crest of a ridge in rear of our fort, so as to interpose a force between our troops and in rear of our batteries. A question had arisen as to whether the assaulting column should consist of white or negro troops; of each, there were brigades in General Burnside's division, which occupied that part of the line nearest to the mine, and therefore seems to have been considered as the command from which the troops to constitute the storming column must be selected. The explosion was destructive to our artillery and its small supporting force immediately above the mine. An opening one hundred fifty feet long, sixty feet wide, and thirty feet deep, suddenly appeared in the place of the earthworks, and the division of the enemy selected for the charge rushed forward to pierce the opening. A Southern writer2 thus describes what ensued:
The white division charged, reached the crater, stumbled over the debris, were suddenly met by a merciless fire of artillery enfilading them right and left and of infantry fusillading them in front; faltered, hesitated, were badly led, lost heart, gave up the plan of seizing the crest in rear, huddled into the crater man on top of man, company mingled with company; and upon this disordered, unstrung, quivering mass of human beings, white and black—for the black troops had followed—was poured a hurricane of shot, shell, canister, musketry, which made the hideous crater a slaughter-pen, horrible and frightful, beyond the power of words. All order was lost; all idea of charging the crest abandoned. Lee's infantry was seen concentrating for the carnival of death; his artillery was massing to destroy the remnants of the charging divisions; those who deserted the crater, to scramble over the debris and run back, were shot down; then all that was left to the shuddering mass of blacks and whites in the pit was to shrink lower, evade the horrible mitraille, and wait for a charge of their friends to rescue them or surrender.