U.S. Grant began the siege of Petersburg, Virginia, on June 20, 1864, bottling up Lee’s army in and around that city. The Union forces cut off all supplies destined for that strategic railhead, a move that would later make starvation a stark reality for Confederate soldiers.
Ambrose E. Burnside, one of the Union commanders, undertook a major effort to break the deadlock at Petersburg. His men devoted weeks to tunneling under a Confederate artillery position. Four tons of black powder were quietly transported to the end of the tunnel and detonated on July 30. The Confederate position was totally destroyed and a huge crater was left in its place. After the smoke cleared, Union forces streamed through the tunnel. The Confederates quickly overcame their confusion and ringed the crater, mowing down wave after wave of advancing foes.
The Battle of the Crater resulted in about 5,300 casualties, mostly Union. Burnside was stripped of his command after this disaster.