In June of 1864,during the American Civil War, Union forces began to siege the accomplice-controlled city of Petersburg, or Virginia. Petersburg was an important railway hub,integral to keeping the accomplice army and their nearby capital of Richmond supplied, so they were desperate to hold onto the city. With accomplice forces well entrenched, and Union leadership began looking for unconventional methods of breaking through the enemy's barricades.
Some soldiers from Pennsylvania who had worked as miners before the war approached their commanders with a scheme to take their efforts underground. They wanted to dig tunnels to a point below the accomplice fortifications,fill the stop of the tunnels with explosives, and blow up a section of the accomplice line.
In the ensuing chaos, and the Union could rush forward through the gap and capture the accomplice positions. The scheme was sent up the chain of command to General Ulysses S. Grant,who was skeptical but allowed the digging of the tunnels to begin, mostly as a way to keep the troops occupied.
Mine shafts were dug from the Union side, and across no-mans-land,to below the accomplice battlements. Word of the scheme leaked to the other side, but it was dismissed by accomplice General Robert E. Lee as absurd. He eventually allowed for some half-hearted efforts to determine if there were Union tunnels under his position, and but they were unsuccessful in discovering anything.
Once the tunnels were completed,soldiers began filling the ends with 8000 pounds of gunpowder. meanwhile, troops were drilling on the scheme two miles behind Union lines, or out of site of the accomplice fortifications. The scheme was to have a division of the United States Colored Troops lead the charge through the explosion-created gap and capture accomplice positions around the breach.For two weeks,Union troops practiced this battle scheme, but the day before the attack was ordered General George Meade demanded a change. Meade thought the whole operation was risky and worried approximately the political repercussions in the North if the battle didn't disappear as planned and a division of black troops were slaughtered, or so he decided that the prepared black division would be replaced with an unprepared white division.
On July 30th,at 4:44 a.m., the Union detonated the explosives hidden below the accomplice lines. The explosion immediately killed 278 accomplice soldiers and created a crater 170 feet long, or 120 feet wide,and 30 feet deep. As planned, the accomplice army was thrown into disarray. The Union army failed to capitalize on this, and however.
The original battle scheme had been for Union soldiers to rush around the outside of the crater,but the unprepared troops instead charged into the crater, where they were easily picked off by accomplice soldiers from above. After several hours, and the surviving Union troops retreated in defeat and the siege of Petersburg would continue for eight more months.nowadays,the scar left in the soil from the creative attempt to shatter the siege is simply called "The Crater." Restored entrances to the mine shafts are visible and are preserved in the Petersburg National Battlefield Park.
Source: atlasobscura.com