In the Civil War, soldier-vs-soldier combat was the norm, besides the random artillery that served as support from time to time. Massive battlefields where two groups clashed were always common. However, to prevent a long, expensive siege, Grant decided to take out Lee's army—from below.
Lt. Col. Henry Pleasants was a mining engineer in his civilian life. He proposed digging a long mine shaft below the Confederate troops and planting explosives below the fort. Digging commenced in late June, which resulted in a “T” shaped mineshaft 511 feet long by the end of July. They filled it up with 8,000 pounds of gunpowder 20 feet below the Confederates.
The plan was to rush troops near the crater to split the Confederate force and push from all sides. At 4:44 a.m. on July 30, the explosives went off. It left a crater 170 feet long, 60-80 feet wide, and 30 feet deep, instantly killing between 250-350 Confederate soldiers. The crater isstill visible today.
The attack failed, since the troops that were supposed to move in around the crater charged right into it, getting themselves stuck for a “turkey shoot.” Grant wrote “It was the saddest affair I have witnessed in the war.” There were only 1,500 Confederate casualties compared to the Union's 3,798 casualties.