After obtaining the permission of Burnside and Grant, Pleasants and his men commenced digging their mine shaft on June 25. The lack of proper equipment made it necessary to improvise tools and apparatus with which to excavate. Mining picks were created by straightening army picks. Cracker boxes were converted into hand-barrows in which the dirt was removed from the end of the tunnel. A sawmill changed a bridge into timber necessary for shoring up the mine. Pleasants estimated the tunnel’s direction and depth by means of a theodolite sent him from Washington. The instrument, although outmoded, served its purpose well: the mine shaft hit exactly beneath the salient at which it was aimed. [Illustration: _Lt. Col. Henry Pleasants, onetime mining engineer and the commanding officer of the 48th Pennsylvania Regiment which dug the tunnel under the Confederate line._] [Illustration: _Cross-section view of the Federal tunnel under the Confederate line. Colonel Pleasants later recalled that “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 and it would amount to nothing.”_] Air tube Air-tight door Fireplace Chimney FEDERAL LINE Established June 18, 1864 Tunnel sloped up to avoid heavy clay Air tube JUNE 25, 1864, Tunnel started 510-8/10 feet JULY 27, 1864, 8,000 lbs. of powder placed here CONFEDERATE LINE JULY 30, 1864, Pegram’s Battery destroyed by explosion One of the most remarkable features of the gallery was the method devised to supply the diggers at the end with fresh air. The longer the tunnel grew, the more serious the problem of ventilation became. It had been considered impossible to dig a tunnel for any considerable distance without spacing shafts at regular intervals in order to replace the polluted air with a fresh supply. This problem had been solved by the application of the simple physical principle that warm air rises. Behind the Union picket line and to the right of the mine gallery, although connected with it, the miners dug a ventilating chimney. Between the chimney and the mine entrance they erected an airtight canvas door. Through that door and along the floor of the gallery they laid a square wooden pipe. A fire was then built at the bottom of the ventilating shaft. As the fire warmed the air it went up the chimney. The draft thus created drew the bad air from the end of the tunnel where the men were digging. As this went out, fresh air was drawn in through the wooden pipe to replace it.