Army of the Potomac

• 1. Introduction

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  The Army of the Potomac was born out of disaster. In the summer of 1861, a raw Union force marched out of Washington, D.C., under Brigadier General Irvin McDowell, expecting a quick victory that would end the rebellion. Instead, at the First Battle of Bull Run, they were routed and sent streaming back toward the capital. That defeat would reshape the entire character of the Union war effort in the East.

  Out of that humiliation came something new. On the 26th of July, 1861, Major General George B. McClellan merged several departments under his command and formally created the Army of the Potomac. What followed over the next four years was one of the most complicated institutional stories of the Civil War: a massive fighting force that changed commanders six times, reorganized its corps repeatedly, absorbed entire armies, and marched through Maryland, Pennsylvania, and the length of Virginia. Who led this army, what its soldiers believed about the war, and how it performed in the bloodiest campaigns of the conflict are the questions worth sitting with.

• 2. An Army Forged From Wreckage

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  McClellan's original assignment in the summer of 1861 was not to command everything. He was given the Division of the Potomac, which bundled together McDowell's Department of Northeast Virginia and Brigadier General Joseph K. Mansfield's Department of Washington. Then on the 26th of July, Nathaniel P. Banks's Department of the Shenandoah was folded in, and the combined force took the name that would carry through the rest of the war.

  The army that McClellan inherited was small by the standards of what it would become. Its nucleus traced directly back to McDowell's force, the men who had lost at Bull Run. President Lincoln, impatient for organization, issued an order on the 13th of March, 1862, dividing the army into five corps commanded by the highest-ranking division commanders. McClellan was unhappy with this arrangement. He had intended to wait until battle had tested his generals before assigning them corps command. The tension between McClellan's preference for deliberate preparation and Lincoln's desire for action would become a defining friction of the army's early years.

  A complicating footnote: the name "Army of the Potomac" had actually belonged first to the Confederate side. General P. G. T. Beauregard commanded a Confederate force by that name at First Bull Run, meaning the Union army defeated there ended up adopting the name of the Confederate force that beat it. That Confederate army was later renamed the Army of Northern Virginia, the force that would be the Union army's primary opponent for the rest of the war under Robert E. Lee.

• 3. Soldiers, Politics, and the Meaning of the War

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  The men who filled the Army of the Potomac came from a wide range of backgrounds. Recruiters drew from Northern cities including New York City, Philadelphia, and New Jersey, pulling in both native-born Americans and immigrants, among them Irish newcomers whose numbers in the United States had grown significantly through the mid-19th century.

  Political divisions ran deep within the ranks. The army's soldiers and officers held differing views on what the war was actually for, whether its purpose was to hold the Union together or to end slavery in the South. As historian John Hennessy noted in 2014, many soldiers in the Army of the Potomac grew sympathetic to the goal of emancipation relatively early, while others struggled to square their opposition to abolition with a war that was increasingly moving in that direction.

  Those tensions were not just personal; they played out in the officer corps. Captain Henry Nicholas Blake of the 11th Massachusetts in the Third Corps spoke openly about his complaints when his regiment was transferred to the Second Corps, which historian Zachery Fry described as a haven for Democratic officers loyal to McClellan. Blake's outspokenness earned him a court-martial. Similar treatment fell on other officers who pushed against the political alignment of the high command. Meanwhile, as historian George C. Rable observed, citizen-officers who had come up outside the West Point system were gradually finding their footing as the war continued, shifting the army's internal culture.

  Through the Gettysburg and Overland campaigns, historian John H. Matsui noted that the army's regiments were a mixture of veteran soldiers, draftees, and men who had enlisted for financial reasons. The war had long since stopped being a conflict that any soldier could fit neatly into a single political category.

• 4. The Campaign That Tested the Second Corps

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  On the 1st of July, 1863, the Second Corps of the Army of the Potomac was assigned to reinforce Union lines around Cemetery Hill at Gettysburg as Lee's Army of Northern Virginia pressed to break through the Union defense. Command of the Second Corps fell temporarily to General Gibbons after the previous commander, General Sickles, was wounded during the fighting.

  General Hancock of the Third Corps encountered the 1st Minnesota regiment, led by Colonel Colvill, with only a few hundred men still standing after the earlier fighting. Despite their losses, Hancock ordered the regiment to advance directly against the Confederate brigade approaching the Union lines. As historian Kreiser noted in 2011, the 1st Minnesota's charge briefly created panic among the halted Confederates. The regiment pushed the advance back. Union artillery added its weight to the effort, and together they stopped the Confederate assault on Cemetery Hill, though at a severe cost in lives.

  By the time Gettysburg ended, the I, II, and III Corps had each suffered losses severe enough to leave them nearly nonfunctional as fighting units. One corps commander, Reynolds, was killed in action. Sickles lost a leg and was permanently removed from the war. Hancock was badly wounded and never fully recovered from his injuries. The scale of that human attrition would force yet another round of reorganization before the army could take the field again.

• 5. Commanders and Constant Reorganization

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  Six men commanded the Army of the Potomac between its formation and the end of the war. McDowell held the position from the 27th of May through the 25th of July, 1861. McClellan then took command on the 26th of July, 1861, and held it until the 9th of November, 1862. Ambrose Burnside followed, and during his tenure he divided the army into four Grand Divisions, each composed of two corps. When Burnside was removed in January 1863, Joseph Hooker replaced him, immediately abolished the Grand Divisions, and created a proper Cavalry Corps by consolidating units that had previously been scattered among infantry divisions in smaller formations.

  Hooker's own tenure ended with George Meade's sudden appointment on the 28th of June, 1863, three days before Gettysburg opened. Meade would hold command through the 28th of June, 1865, the longest tenure of any Army of the Potomac commander.

  The structural changes tracked closely with each command transition. By March 1864, after the XI and XII Corps had been sent west in late 1863 to support the Chattanooga campaign, and after the I and III Corps were disbanded following their catastrophic losses at Gettysburg, the army reorganized around just four corps: the II, V, VI, and the Cavalry. When Ulysses S. Grant launched the Overland Campaign, Burnside's IX Corps accompanied the army in a parallel role before being formally absorbed on the 24th of May, 1864. Proximity to Washington and the major Northern cities had given the Army of the Potomac more media coverage than any other Union field army; it also meant the army absorbed more public scrutiny with every defeat, every command change, and every reorganization.

• 6. After the Guns Fell Silent

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  The Army of the Potomac was officially disbanded on the 28th of June, 1865, shortly after participating in the Grand Review of the Armies in Washington, D.C. The Confederate Army of Northern Virginia, the force it had fought across Virginia, Maryland, and Pennsylvania for four years, had already surrendered in April.

  In 1869, veterans founded the Society of the Army of the Potomac as a formal association to preserve the connections built during the war. The society held reunions for decades, carrying forward the shared memory of those campaigns until its last gathering in 1927. That final reunion came more than sixty years after the army's disbandment, long enough that the men attending had spent most of their lives in the peace the army had helped create.