Its dual mission was to defeat the Confederate Army of Northern Virginia and to safeguard Washington, D.C. The army was also known as “Mr. Lincoln’s Army” for its close association with the sitting United States president. It was formed from the Army of Northeastern Virginia, which, under Brigadier General Irvin McDowell, had suffered a humiliating defeat near Manassas Junction, Virginia, on July 21, 1861. Four days after the debacle, McDowell was replaced by Major General George B. McClellan, the victor in several small but well-publicized actions in western Virginia. On July 26, 1861, the Department of the Shenandoah, commanded by Major General Nathaniel P. Banks, was merged with McClellan’s forces, and McClellan formed the Army of the Potomac, which was composed of all military forces in the former Departments of Northeastern Virginia, Washington, Baltimore, and the Shenandoah.
First headquartered on the Virginia Peninsula, and later, just outside Washington, D.C., the Army of the Potomac when through a series of commanders including George McClellan, Ambrose Burnside, Joseph Hooker, George Gordon Meade, and General Ulysses S. Grant.
The army survived its succession of commanders and battlefield reverses to attain final victory. In the spring of 1862, during the mismanaged Peninsula Campaign, the Army of the Potomac failed to capture the Confederate capital at Richmond. That summer, some of its components met defeat in the Second Manassas Campaign. Although it blunted Robert E. Lee’s September 1862 invasion of Maryland, it gained only a tactical draw against the smaller but superbly led Confederate army. Three months later, the army suffered horrific losses at Fredericksburg, and the following May, it was routed by General Robert E. Lee at Chancellorsville. In July 1863, however, it gained a critical victory at Gettysburg, Pennsylvania, ending Lee’s second invasion of the North.
Beginning early in May 1864, the army methodically advanced against Richmond, Virginia, and equally strategic Petersburg, suffering heavy losses at every turn. Compelled to besiege both cities, the Army of the Potomac eventually forced their evacuation and Lee’s retreat. As a result, on April 9, 1865, realizing that he had been overtaken, General Robert E. Lee surrendered to General Ulysses S. Grant. at Appomattox, Virginia, effectively ending the Civil War. After the end of the war, it was disbanded on June 28, 1865, shortly following its participation in the Armies’ Grand Review.