By far the most unusual event during the siege of Petersburg was the attempt by Grant to take Petersburg by a huge mining operation.
The idea of the tunnel was devised by Lieutenant Colonel Henry Pleasants, the 33 year old commanding officer of the 48th Pennsylvania. Pleasants was a mining engineer in civilian life and many of his men were coal miners. He became convinced that his men could dig a tunnel under the Confederate fort known as Elliot’s Salient, then fill a mine under the fort sufficient to blow it to kingdom come, along with nearby Confederate trenches. Pleasants took the idea to his corps commander Major General Ambrose Burnside. He and his men had received permission, but he received virtually no assistance from the rest of the Army in the digging of the tunnel, he and his men having to improvise everything they used. Engineering officers told Pleasants that he was crazy and at 511 feet the tunnel would be too long and his men would die of asphyxiation digging the tunnel long before it could be completed.
The tunnel was elevated as it advanced toward the Confederate fort to prevent moisture clogging it up. Fresh air was pumped in by air-exchange mechanism near the entrance. Pleasants had constructed a ventilation shaft located well behind Union lines, and connected it to the mine with canvas. At the shaft’s base, a fire was kept continuously burning. A wooden duct ran the entire length of the tunnel which protruded into the outside air. The fire heated stale air inside of the tunnel, forcing it up the ventilation shaft and out of the mine. The resulting vacuum then sucked fresh air in from the mine entrance via the wooden duct which transported the fresh air to the digging miners.
The took took a bit over two weeks to dig and the mine fifty feet under the Confederate fort took almost another two weeks to construct. It was filled with four tons of gunpowder. The Confederates attempted some desultory countermining operations, but the Union tunnel troops went about their work undiscovered. By July 28, 1864 the mine was ready to explode whenever the high command gave the word. That word would be given on July 30, 1864.
Here is a portion of an article on the tunneling operation that led up to the Battle of the Crater, written by Major William H. Powell, United States Army, which appeared in volume 4 of Battles and Leaders of the Civil War.
BY the assaults of June 17th and 18th, 1864, on the Confederate works at Petersburg, the Ninth Corps, under General Burnside, gained an advanced position beyond a deep cut in the railroad, within 130 yards of the enemy’s main line and confronting a strong work called by the Confederates Elliott’s Salient , and sometimes Pegram’s Salient. In rear of that advanced position w as a deep hollow. [See map, p. 538.) A few days after gaining this position Lieutenant-Colonel Henry Peasants, who had been a mining engineer and Who belonged to the 48th Pennsylvania Volunteers, composed for the most part of miners from the upper Schuylkill coal region, suggested to his division commander, General Robert B. Potter, the possibility of running a mine under one of the enemy’s forts in front of the deep hollow. This proposition was submitted to General Burnside, who approved of the measure, and work was commenced on the 25th of June. It ever a man labor ed under disadvantages, that man was Colonel Peasants. In his testimony before the Committee on the Conduct of the War he said :
“My regiment was only about four hundred strong. At first I employed but a few men at a time, but the number was increased as the work progressed, until at last I had to use the whole regiment-non-commissioned officers and all. The great difficulty I had was to dispose of the material got out of the mine. I found it impossible to get any assistance from anybody ; I had to do all the work move all the earth in old cracker-boxes ; I got pieces of hickory and nailed on the boxes in which we received our crackers, and then iron-clad them with hoops of iron taken from old pork and beef barrels. . . . Whenever I made application I could not get anything, although General Burnside was very favorable to it. The most important thing was to ascertain how far I had to mine, because if I fell short of or went beyond the proper place, the explosion would have no practical effect. Therefore I wanted an accurate instrument with which to make the necessary triangulations. I had to make them on the farthest front line, where the enemy’s sharp-shooters could reach me. I could not get the instrument I wanted, although there was one at army headquarters, and General Burnside had to send to Washington and get an old-fashioned theodolite, which w as given to me. . . . General Burnside told me that General Meade and Major Duane, chief engineer of the Army of the Potomac, said the thing could not be done-that it was all clap-trap and nonsense; that such a length of mine had never been excavated in military operations, and could not be ; that I would either get the men smothered, for want of air, or crushed by the falling of the earth; or the enemy would find it out aud it would amount to nothing. I could get no boards or lumber supplied to me for my operations. I had to get a pass and send two companies of my own regiment, with wagons, outside of our lines to rebel saw-mills, and get lumber in that way, after having previously got what lumber I could by tearing down an old bridge. I had no mining picks furnished me, but had to take common army picks and have them straightened for my mining picks. . . . The only officers of high rank, so far as I learned, that favored the enterprise were General Burnside, the corps commander, and General Potter, the division commander.”
On the 23d of July Colonel Pleasants had the whole mine ready for the powder. With proper tools and instruments it could have been done in one-third or one-fourth of the time. The greatest delay was occasioned by taking out the material, which had to be carried the whole length of the gallery. Every night the pioneers of Colonel Pleasants’s regiment had to cut bushes to cover the fresh dirt at the mouth of the gallery ; otherwise the enemy could have observed it from trees inside his own lines.
The main gallery was 510 8/10 feet in length. The left lateral gallery was thirty-seven feet in length and the right lateral thirty-eight feet. The magazines, eight in number, were placed in the lateral galleries – two at each end a few feet apart in branches at nearly right angles to the side galleries and , two more in each of the side galleries similarly placed by pairs, situated equidistant from each other and the end of the galleries.
It had been the intention of General Grant to make an assault on the enemy’s works in the early part of July; but the movement was deferred in consequence of the work on the mine, the completion of which was impatiently awaited. As a diversion Hancock’s corps and two divisions of cavalry had crossed to the north side of the James at Deep Bottom and had threatened Richmond. A part of Lee’s army was sent from Petersburg to checkmate this move, and when the mine was ready to be sprung Hancock was recalled in haste to Petersburg.
When the mine was ready f or the explosives General Meade requested General Burnside to submit a plan of attack. This was done in a letter dated July 26th, 1864, in which General Burnside said :
” . . . It is altogether probable that the enemy are cognizant of the fact that we are mining, because it is mentioned in their papers, and they have been heard at work on what are supposed to be shafts in close proximity to our galleries. But the rain of night before last has, no doubt, much retarded their work. We have heard no sound of workmen in them either yesterday or to-day ; and nothing is heard by us in the mine but the ordinary sounds of work on the surface above. This morning we had some apprehension that the left lateral gallery was in danger of caving in from the weight of the batteries above it and the shock of their firing. But all possible precautions have been taken to strengthen it, and we hope to preserve it intact. The placing of the charges in the mine will not involve the necessity of making a noise. It is therefore probable that we will escape discovery if the mine is to be used within two or three days.
It is, nevertheless, highly important, in my opinion, that the mine should be exploded at the earliest possible moment consistent with the general interests of the campaign. . . . But it may not be improper for me to say that the advantages reaped from the work would be but small if hout any cooperative movement.
” My plan would be to explode the mine just before daylight in the morning or at about 5 o’clock in the afternoon; mass the two brigades of the colored division in rear of my first line, in columns of division ‘ double-columns closed in mass,’-the head of each brigade resting on , the front line, and, as soon as the explosion has taken place, move them forward, with instructions for the divisions to take half distance, and as soon as the leading regiments of the two brigades pass through the gap in the enemy’s line, the leading regiment of the right brigade to come into line perpendicular to the enemy’s line by the ‘ right companies on the right into line, wheel,’ the left companies on the right into line, and proceed at once down the line of the enemy’s works as rapidly as possible ; and the leading regiment of the left brigade to execute the reverse movement to the left, moving up the enemy’s line. The remainder of the columns to move directly toward the crest in front as rapidly as possible, diverging in such a way as to enable them to deploy into column of regiments, the right column making as nearly as possible for Cemetery Hill; these columns to be followed by the other divisions of the corps as soon as they can be thrown in. This would involve the necessity of relieving these divisions by other troops before the movement, and of holding columns of other troops in readiness to take our place on the crest, in case we gain it, and sweep down it. It would, in my opinion, be advisable, if we succeed in gaining the crest, to throw the colored division right into the town. There is a necessity for the cooperation, at least in the way of artillery, by the troops on our right and left. OI the extent of this you will necessarily be the judge. I think our chances of success, in a plan of this kind, are more than even.” . . .