United States Armies in the East

The Army of the Potomac – officially known as the Department of the Potomac – was the main field army of the United States in the Eastern Theater for most of the Civil War. It was tasked with protecting the national capital of Washington and with capturing the Confederate capital of Richmond. In the end, its mission simply became the destruction of its opponent for the entire war, Robert E. Lee’s Army of Northern Virginia.

The Army of the Potomac was created in July of 1861 from the wreckage of the army Irvin McDowell had led to Bull Run. The Departments of Annapolis, Pennsylvania and the Shenandoah were merged together, giving George McClellan command of most of the Eastern Theater, while tens of thousands of new recrtuits poured in from the northern states. McClellan created a grand army that he would never have the nerve to properly use, but which would ultimately prevail due to its ability to outlast both its enemies and leaders.

This site shows the organization of the Army of the Potomac down to the regiment and battery level for each month of the war. These are linked to unit histories for most units and biographies of many of the leaders.

McClellan’s Army • August 1861 – October 1862
Union Major General George McClellan

George McClellan

McClellan takes command. The new recruits are organized and trained, formed into brigades and then divisions. Lincoln forces the creation of army corps as McClellan launches the Penninsula Campaign. After the failure of the campaign the army returns to Washington to save the capital after Pope’s Army of Virginia was defeated at Second Bull Run. McClellan halts Lee’s invasion of the North as he leads the Army of the Potomac to its bloodiest day at Antietam, but afterwards Lincoln cannot force him to move. McClellan is removed, and Ambrose Burnside reluctantly accepts command.

1861: AugustSeptemberOctober •  NovemberDecember
1862: JanuaryFebruaryMarchAprilMayJuneJuly • AugustSeptemberOctober 

Burnside’s Army • November 1862 – January 1863
Union Major General Ambrose Burnside

Ambrose Burnside

Ambrose Burnside surprised everyone with a rapid march to the Rapahannock. But the army came to a dead halt when critical bridging equipment was left behind. With surprise lost and Lee dug on the Fredericksburg bluffs, Burnside insisted on continuing with the plan, with horrific results. A follow-up offensive sank into the January mud, and with the army near mutiny Burnside was replaced by the confident and caustic Joseph Hooker.

November 1862 • DecemberJanuary 1863

Hooker’s Army • February – June 1863
Union Major General Joseph Hooker

Joseph Hooker

To the surprise of many, Hooker turned the army around. He provided fresh vegetables and meat, back pay and corps badges. Within a short time the army’s confidence was soaring and they were looking for a fight. Hooker provided that as well, with a good plan that stole a march on Robert E. Lee and might have done everything that Hooker was boasting if he had not had a crisis of confidence that lost him the Battle of Chancellorsville. Hooker followed up Lee’s resulting invasion of the north, but the fighting with Washington became more fierce than that with Lee, and Hooker asked to be relieved. He was, and George Meade took over the Army just hours before the greatest battle of the war.

1863: FebruaryMarchAprilMayJune

Meade’s Army  • June 1863 – June 1865
Union Major General George Meade

George Meade

As Lee invades the North for a second time George Meade takes over the army in mid-campaign. He wins the war’s biggest and most costly battle at Gettysburg but the victory is incomplete. He cannot gain an advantage in the fall campaigns back south of the Potomac. Two army corps are permanently detached to the Western Theater. The army consolidaties its five army corps into three, and the Ninth Corps rejoins from the west. With the new commander in chief, Ulysses Grant, looking over Meade’s shoulder, a series of terrible battles returns the army to the gates of Richmond. Finally, the long Siege of Petersburg wears down Lee’s army and leads to its surrender at Appomattox.

1863: July • AugustSeptemberOctober • NovemberDecember
1864: January • FebruaryMarchAprilMayJune • July • AugustSeptemberOctober • NovemberDecember
1865: January • FebruaryMarchAprilMayJune