Digging the Petersburg Mine, I

 Some details from the September 1909 issue of Confederate Veteran . . .

Col. Henry Clay Pleasants

THE "PETERSBURG MINE."

 BY WILLIAM R. D. BLACKWOOD, BREVET BRIGADIER GENERAL UNITED STATES VOLUNTEER ENGINEERS.

When the siege lines of the Federal army had been established in front of Petersburg, it was seen that a direct frontal attack on the Confederate positions could not result in their capture unless at a loss of life which would be unjustifiable even if successful. The alternative was to block the route of supplies by way of the Southside Railroad and to make the matter one of endurance on both sides — a long and tedious method. I do not use space as to what was done in other directions, but will come at once to the mine.

While looking at the Confederate defenses near the so-called "Elliot salient" Lieut. Col. Henry Pleasants, of the 48th Pennsylvania Volunteers, saw that if that part of the defenses was destroyed the whole line for about a mile around must be untenable, because it dominated the works on either side for that distance. The Colonel and myself were close friends; and as we had but three engineers in the 9th Corps — Captain Poe, of the Regulars, Colonel Pleasants, of the 48th, and myself, also of the 48th — he and I were naturally interested in anything of that nature. He discussed the problem with me long before talking with others. Although surgeon of the 48th and brigade surgeon at the time, I had been for a year prior the engineer of the second division work, the regimental medical work being in charge of my two assistant surgeons. I agreed with the Colonel that the plan was not only feasible, but just the thing we needed to break the Confederate Inns at that vulnerable and important position, and then he interviewed some of the higher officers of the army, all of whom except General Grant, who was noncommittal, decried the ability of any one to successfully mine the works at such a distance, giving varied and illogical reasons therefor. The main difficulty in the mind of the engineers was the problem of ventilation, which was really no difficulty at all. We never had trouble of that nature after we entered the drift.

After a great delay we gut permission to go ahead, and we did. The men of the regiment wen with very few exceptions practical coal miners from Schuylkill County. We began the proximal end in a cut which afforded cover from the view of the Confederates, and it gave us the valuable assistance of a covered way through which to carry away the excavated drift. Ten triangulations gave us the actual distance of five hundred and thirty eight feet. The tunnel was originally intended to run in a straight axial line till under the salient; but difficulties cropped up as we progressed, compelling us to depart from the direct course, one of which was a sand slip which obliged us to turn the drift upward at an angle of six degrees for a distance of sixty feel, when we again resumed direct course. Much of the tunnel was lined with logs to keep up the roof, and the height of the drift was between three and four feet— the width always four feet.

The following statement will give some idea of the problem to be met: Height of Confederate terreplein above our works, 32 feet; drop into ravine behind Federal works, 29 feet; level of excavation from ravine bottom, 12 feet ; ultimate elevation of ascending slope, 17 feet;  angle of sections 1, 2, 3, relatively, 15 degrees, 42 degrees, and 11 degrees; extreme length of tunnel, as stated, 538 feet; length of laterals, 154 feet; deviation angle between sections 1 and 2, 12 degrees; number of triangulations, 10; control or proving triangulations, 4; amount of powder used in magazines, 4 1/2 tons; energy in foot pounds of power, 27,852,000; measured height of impulse, 498 vertical feet; cubic feet of earth removed from tunnel, 91,898; estimated cubical displacement of earth in crater, 456,000 tons. The mine was begun on June 25, 1864. and completed on July 27. The powder was installed on July 28 and the mine exploded on the 30th at 5:20 a.m. 

The ventilation of the tunnel was obtained by running a flue eight inches square along the floor of the drift extending from the outlet to the breast where the men were working which carried fresh air from the exterior to the breast in this manner. A fire was constantly burning in a chamber just outside the entrance of the drift, and the flue referred to was connected with the ash pit, and thus fed the fire with air brought from the extreme end or breast of the tunnel. So that fresh air flowed in through the exterior opening. The dirt removed was principally heavy clay of many colors and was called "Powhatan Clay." The men made various articles from this clay, such as pipes, miniature mortars, etc., and one very elaborate pipe was given to General Grant, which he prized highly. The dirt removed was ultimately placed on the parallels far from the mine, and was taken from the ravine only at night.

Nobody except the men of the 48th was permitted to work on the mine. Since the close of the war a considerable number of fakirs have claimed to be the originators of the mine, but they are impostors. Colonel Pleasants alone conceived the idea, and as his assistant engineer I know all about it. Pleasants was gentleman of high extraction, a soldier of extreme bravery, and a man of the highest honor, he did what never was done in the history of war before or since till this day — conceived and carried to a successful end the greatest mine ever built in the annals of military engineering — and to him alone is due the credit. The mine was ten times longer than the longest previous mine ever built.

(TO BE CONTINUED)