On April 4, Lincoln created the Department of the Rappahannock, detaching the I Corps from the Army of the Potomac to form the core of the new department, and giving command of the department to I Corps commander, Irvin McDowell.
In May, Franklin’s division was detached and sent south to reinforce McClellan in his Peninsula campaign, uniting with a division of the IV Corps to form the VI Corps.[2]
On June 18, McCall’s division, the “Pennsylvania Reserves”, was also detached and sent to join McClellan’s army on the Virginia Peninsula. Temporarily attached to the V Corps, it saw heavy action at Gaines' Mill and Glendale. Division commander Brig. Gen. George McCall and future I Corps commander Brig. Gen. John Reynolds were both captured and freed in a prisoner exchange that August.
On June 26, Rufus King’s division, James B. Ricketts’ division, and Abner Doubleday’s brigade were transferred from the Department of the Rappahannock to the newly created Army of Virginia, forming its III Corps, under the command of Irvin McDowell.[3]
On August 26, the “Pennsylvania Reserves” were transferred to the III Corps of the Army of Virginia and fought at the Second Battle of Bull Run. Soon after the battle, the corps was transferred to the Army of the Potomac and reclassified as the I Corps of the Army of the Potomac.[4]
Maj. Gen. Joseph Hooker
In early September, the I Corps, now under the command of Major General Joseph Hooker, followed Lee through Maryland and fought at South Mountain and Antietam. John Reynolds (who had been elevated to division command of the Reserves) was temporarily detached to train militia troops in his home state of Pennsylvania and did not participate in the Maryland Campaign. At Antietam, the I Corps was the first corps engaged, and suffered enormous losses in the fighting around the cornfield and Dunker Church. Hooker was wounded in the foot during the battle and command of the I Corps devolved on George Meade (the ranking division commander). In October, Reynolds returned and was made commander of the corps.
Having fought three battles in six weeks, the I Corps was severely depleted. An influx of new volunteer regiments (both three year and nine month) arrived to replenish its ranks, and by November it was back up to full strength.
The corps moved southward to fight General Robert E. Lee's army at the Battle of Fredericksburg, commanded by Major General John F. Reynolds, arguably the best Union corps commander in the Eastern Theater. At Fredericksburg, Meade and John Gibbon's divisions fought Stonewall Jackson's corps south of the town while Doubleday's division was held in reserve. The I Corps did not see any significant action in the Chancellorsville Campaign.
"The Fall of Reynolds" – drawing of Reynolds' death at Gettysburg
In its last major battle, the Battle of Gettysburg, General Reynolds was killed just as the first troops arrived on the field, and command was inherited by Major General Abner Doubleday. Although putting up a ferocious fight, the I Corps was overwhelmed by the Confederate Third Corps (A.P. Hill) and Robert E. Rodes's division of Richard S. Ewell's Second Corps. It was forced to retreat through the town of Gettysburg, taking up defensive positions on Cemetery Hill after the 16th Maine's brave stand of which only 39 soldiers returned. The next day (July 2, 1863), the command was given to Major General John Newton, a division commander from the VI Corps. This was a controversial move that deeply offended the more senior Doubleday. Newton led it through the remainder of the battle, including the defense against Pickett's Charge, and through the Mine Run Campaign that fall.
On March 24, 1864, the Civil War career of the I Corps came to an end as it was disbanded and its depleted units were reorganized into two divisions, which were transferred into the V Corps of the Army of the Potomac.
The Army of Northern Virginia was the primary military force of the Confederate States of America in the Eastern Theater of the American Civil War. It was also the primary command structure of the Department of Northern Virginia. It was most often arrayed against the Union Army of the Potomac.
George Gordon Meade was a United States Army Major General who commanded the Army of the Potomac during the American Civil War from 1863 to 1865. He fought in many of the key battles of the Eastern theater and defeated the Confederate Army of Northern Virginia led by General Robert E. Lee at the Battle of Gettysburg.
Joseph Hooker was an American Civil War general for the Union, chiefly remembered for his decisive defeat by Confederate General Robert E. Lee at the Battle of Chancellorsville in 1863.
The Army of the Potomac was the principal 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.
Irvin McDowell was a career American army officer. He is best known for his defeat in the First Battle of Bull Run, the first large-scale battle of the American Civil War. In 1862, he was given command of the I Corps of the Army of the Potomac. He fought unsuccessfully against Thomas "Stonewall" Jackson's troops during the Valley Campaign of 1862, and was blamed for contributing to the defeat of United States troops at the Second Battle of Bull Run in August.
John Fulton Reynolds was a career United States Army officer and a general in the American Civil War. One of the Union Army's most respected senior commanders, he played a key role in committing the Army of the Potomac to the Battle of Gettysburg and was killed at the start of the battle.
The Army of Virginia was organized as a major unit of the Union Army and operated briefly and unsuccessfully in 1862 in the American Civil War. It should not be confused with its principal opponent, the Confederate Army of Northern Virginia, commanded by Robert E. Lee.
James Samuel Wadsworth was a philanthropist, politician, and a Union general in the American Civil War. He was mortally wounded in battle during the Battle of the Wilderness of 1864.
The V Corps was a unit of the Union Army of the Potomac during the American Civil War.
The Maryland campaign occurred September 4–20, 1862, during the American Civil War. Confederate Gen. Robert E. Lee's first invasion of the North was repulsed by the Army of the Potomac under Maj. Gen. George B. McClellan, who moved to intercept Lee and his Army of Northern Virginia and eventually attacked it near Sharpsburg, Maryland. The resulting Battle of Antietam was the bloodiest single-day battle in American history.
The eastern theater of the American Civil War consisted of the major military and naval operations in the states of Virginia, West Virginia, Maryland, and Pennsylvania, the District of Columbia, and the coastal fortifications and seaports of North Carolina.
Marsena Rudolph Patrick was a college president and an officer in the United States Army, serving as a general in the Union volunteer forces during the American Civil War. He was the provost marshal for the Army of the Potomac in many of its campaigns.
The 22nd Regiment Massachusetts Volunteer Infantry was an infantry regiment in the Union army during the American Civil War. The 22nd Massachusetts was organized by Senator Henry Wilson and was therefore known as "Henry Wilson's Regiment." It was formed in Boston, Massachusetts, and established on September 28, 1861, for a term of three years.
The following Union Army units and commanders were the initial structure on April 4, 1862 of the Union Department of the Potomac during the Peninsula campaign of the American Civil War. This list includes units deployed to the Virginia Peninsula, and those that remained in the Washington area. The Confederate order of battle is listed separately.
The 1st Pennsylvania Reserve Regiment, also known as the 30th Pennsylvania Volunteer Infantry, was a regiment in the Union Army during the American Civil War. It was a part of the famed Pennsylvania Reserve division in the Army of the Potomac for much of the war, and served in the Eastern Theater in a number of important battles, including Antietam, Fredericksburg, and Gettysburg.
The 5th Pennsylvania Reserve Regiment also known as the 34th Pennsylvania Volunteer Infantry was an infantry regiment that served in the Union Army as part of the Pennsylvania Reserves infantry division during the American Civil War.
The 9th Pennsylvania Reserve Regiment also known as the 38th Pennsylvania Volunteer Infantry was an infantry regiment that served in the Union Army as part of the Pennsylvania Reserves infantry division during the American Civil War.
The 10th Pennsylvania Reserve Regiment also known as the 39th Pennsylvania Volunteer Infantry was an infantry regiment that served in the Union Army as part of the Pennsylvania Reserves infantry division during the American Civil War.
Battery "B", 4th Regiment of Artillery was a light artillery battery that served in the Union Army during the American Civil War.
The Department of the Rappahannock was a department of the Union Army in the Eastern Theater of the American Civil War that existed from April 4 to June 26, 1862.
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