Cold Harbor, Battle of, June 1–3, 1864, a battle of the American Civil War. It was fought about 10 miles (16 km) northeast of Richmond, Virginia. The Union Army of the Potomac under General U. S. Grant, numbering about 100,000 men, opposed the Confederate force of about 65,000 led by General Robert E. Lee. Grant tried without success to find a weak spot in the Confederate lines during several days of probing attacks. Finally, on the morning of June 3, the Union forces moved forward against the Confederate lines in a frontal assault.

The Union troops were driven back within 30 minutes. Within an hour the Union forces withdrew, after losing about 7,000 men without having made any headway. The total Union losses during the whole period of this battle exceeded 12,000 men, while the Confederate losses probably did not exceed 2,500. Military experts have agreed that the assault at Cold Harbor was the greatest mistake of Grant's career.