The brainchild of Union Colonel Henry Pleasants. Late in the American Civil War, Pleasants, a mining engineer by trade proposed a radical plan to his commanding officers. The plan involved digging a tunnel under the Confederate line at Petersburg, Virginia and exploding a charge in the middle of Robert E. Lee's entrenched forces there. It took about twenty-eight days, but eventually the tunnel was completed, despite the fact that the Confederates had a sense of what was going on and attempted to dig their own tunnels to counter.
As planned, on July 30, 1864, the planted charge blew a 500 yard wide hole in the midst of Lee's line. However, poor planning made the resulting attack a debacle. No scaling ladders were available and the walls of the crater could not be climbed with any degree of ease. Exhausted Union troops trapped in the crater were slaughtered by the Confederates and the operation was labelled a total and "stupendous" failure by Ulysses S. Grant, who was in command.