The First Corps was a significant military unit in the United States Army during the American Civil War. Established in 1861, it played a crucial role in many key battles, including the Battle of Gettysburg and the Battle of Antietam. The corps was known for its leadership under notable commanders like John F. Reynolds and Joseph Hooker. Initially part of the Army of the Potomac, the First Corps was involved in various campaigns throughout the war. It was reorganized multiple times and eventually disbanded in 1865 after the war's conclusion. The corps contributed to the Union's overall strategy and success in the conflict.