The Army of the Potomac was the primary field army of the Union army in the eastern theater of the American Civil War. It was created in July 1861 shortly after the First Battle of Bull Run and was disbanded in June 1865 following the surrender of the Confederate Army of Northern Virginia in April.
The Army of the Potomac was founded in 1861. It initially was only the size of a corps relative to the size of Union armies later in the Civil War. Its nucleus was called the Army of Northeastern Virginia led by Brig. Gen. Irvin McDowell. It fought and lost the Civil War's first major battle, the First Battle of Bull Run. The arrival in Washington, D.C., of Maj. Gen. George B. McClellan dramatically changed the makeup of that army. McClellan's original assignment was to command the Division of the Potomac, which included the Department of Northeast Virginia under McDowell and the Department of Washington under Brig. Gen. Joseph K. Mansfield.
On July 26, 1861, the Department of the Shenandoah, commanded by Maj. Gen. Nathaniel P. Banks, was merged with McClellan's departments and on that day, McClellan formed the Army of the Potomac, which was composed of all military forces in the former Departments of Northeastern Virginia, Washington, Pennsylvania, and the Shenandoah. The men under Banks's command became an infantry division in the Army of the Potomac. The army started with four corps, but these were divided during the Peninsula campaign to produce two more. After the Second Battle of Bull Run, the Army of the Potomac absorbed the units that had served under Maj. Gen. John Pope.
The belief that John Pope commanded the Army of the Potomac in the summer of 1862 after McClellan's unsuccessful Peninsula campaign is mistaken. On the contrary, Pope's Army of Virginia was built around different units, although three corps of the Army of the Potomac were sent to northern Virginia and were under Pope's operational control during the Northern Virginia campaign. During the time that the Army of Virginia existed, the Army of the Potomac was headquartered on the Virginia Peninsula, and then outside Washington, D.C., with McClellan still in command, although most of his troops had been temporarily reassigned. After Pope's defeat at Second Bull Run, McClellan was given back his original units, plus most of the units of the Army of Virginia, which were integrated into the Army of the Potomac – although not always successfully.
The Army of the Potomac underwent many structural changes during its existence. The army was divided by Ambrose Burnside into three grand divisions of two corps each with a Reserve composed of two more. Hooker abolished the grand divisions. Thereafter the individual corps, seven of which remained in Virginia, reported directly to army headquarters. Hooker also created a Cavalry Corps by combining units that previously had served as smaller formations. In late 1863, two corps were sent West, and – in 1864 – the remaining five corps were recombined into three. Burnside's IX Corps, which accompanied the army at the start of Ulysses S. Grant's Overland Campaign, rejoined the army later. For more detail, see the section Corps below.
The Army of the Potomac fought in most of the Eastern Theater campaigns, primarily in (Eastern) Virginia, Maryland, and Pennsylvania. After the end of the war, it was disbanded on June 28, 1865, shortly following its participation in the Grand Review of the Armies.
The Army of the Potomac was also the name given to General P. G. T. Beauregard's Confederate army during the early stages of the war (namely, First Bull Run; thus, the losing Union army ended up adopting the name of the winning Confederate army). However, the name was eventually changed to the Army of Northern Virginia, which became famous under General Robert E. Lee.
In 1869, the Society of the Army of the Potomac was formed as a veterans association. It had its last reunion in 1927.
The Army of the Potomac was a Union regiment used throughout the Eastern Theater of the American Civil War. Though their military achievement throughout the Eastern Theater can be attributed to capable Union leadership, the Army of the Potomac, particularly the army’s average infantrymen, contributed much to the Union’s military success and political realignment, as the war’s motivation shifted towards ending slavery.
Soldiers and their Political Stance
Like most regiments in the Union Army, the Army of the Potomac was made up of individual soldiers from various social and political backgrounds, each contributing to the army’s performance and legacy. The army recruited soldiers from Northern cities such as New York City, Philadelphia, and New Jersey, pulling soldiers from both native and foreign-born populations such as the Irish immigrant population which had risen significantly in the U.S throughout the mid 19th century. Along with their diverse origins, the soldiers of the Potomac Army came from various political backgrounds and shared differing beliefs on the war’s objectives and political stance, with the army shifting allegiances between the Copperhead Democrats and Republicans throughout the war.
As the American Civil War progressed, political tensions among army generals and officers became common, with complaints over McClellan’s affiliation with the Copperhead movements drawing criticism from lower officers. Capt. Henry Nicholas Blake of the 11th Massachusetts in the Third Corps drew considerable complaints over the regiments of transfer into the Second Corps, with US historian Zachery Fry describing it as a haven for Democratic officers loyal to General McClellan. These comments eventually landed Blake a court-martial, with other officers within the Army of the Potomac receiving similar treatment by high command. Complaints also arose as the influence from West Point and other high-standing institutions waned, with historian George C. Rable highlighting how citizen-officers were coming into their own role as the war continued.
Most low-ranking officers and Union soldiers throughout the war would share similar complaints over the leadership of General McClellan along with other Copperhead Democrats that made up the Army of the Potomac’s leadership. This occurred as changes in mindset over the war’s desired outcome came into question, whether it was a war to keep the Union together or for the emancipation of slaves in the South, with soldiers attempting to construct a meaning for their contributions to the war effort. According to Hennessy (2014), while many soldiers in the Army of the Potomac grew sympathetic with the goal of emancipation early on, others within the army struggled to reconcile with their own opposition over abolition despite the war shifting towards slavery’s end. As the war continued, Union soldiers and some low-ranking officers grew willing to express their feelings over political affairs related to the war’s outcome while most high-ranking generals remained silent on these cases.
Soldiers during the Gettysburg and Overland campaign
During the Battle of Gettysburg on July 1st, 1863, the Second Corp of the Army of the Potomac were tasked with reinforcing Union lines around Cemetery Hill from Lee’s Army, who attempted to extend Union positions and create a breakthrough in the Union’s defense. General Gibbons was given temporary command of the Second Corps after their previous commanding officer, General Sickles was wounded during the engagement. The Second Corp, along with support from General Hancock of the Third Corp held their positions against the Confederate advance on Cemetery Hill, with these regiments attempting to patch the Union’s defensive lines, with historians such as John H. Matsui citing how these regiments were made up of a mix between veteran soldiers, draftees, along with men who enlisted with the benefit of monetary gain.
As the fighting continued, General Hancock of the Third Corps ran into the 1st Minnesota regiment led by Colonel Colvill, with the remaining regiment numbering around a few hundred strong. Despite their loses over the battle, the men seemed willing to continue the fight against the Confederate assault as General Hancock ordered the regiment to advance on the Confederate Brigade approaching the Union lines. According to Kreiser (2011), the soldiers proved themselves capable of pushing the Confederates back, using the element of surprise as “their advance briefly created a ripple of panic among some of the now halted Confederates.” The 1st Minnesota regiment, followed by support from Union artillery, was successful at halting the Confederate assault on the hill, despite coming at a high human cost.