I Corps (First Corps) was the designation of three different

corps Corps (; plural ''corps'' ; from French , from the Latin "body") is a term used for several different kinds of organization. A military innovation by Napoleon I, the formation was formally introduced March 1, 1800, when Napoleon ordered Gener ...

-sized units in the Union Army during the

American Civil War The American Civil War (April 12, 1861May 26, 1865; also known by Names of the American Civil War, other names) was a civil war in the United States between the Union (American Civil War), Union ("the North") and the Confederate States of A ...

. Separate formation called the I Corps served in the

Army of the Ohio The Army of the Ohio was the name of two Union Army, Union armies in the American Civil War. The first army became the Army of the Cumberland and the second army was created in 1863. History 1st Army of the Ohio General Orders No. 97 appointed ...

Army of the Cumberland The Army of the Cumberland was one of the principal Union armies in the Western Theater during the American Civil War. It was originally known as the Army of the Ohio. History The origin of the Army of the Cumberland dates back to the creatio ...

under Alexander M. McCook from September 29, 1862 to November 5, 1862, in the

Army of the Mississippi Army of the Mississippi was the name given to two Union armies that operated around the Mississippi River, both with short existences, during the American Civil War. History 1862 The first army was created on February 23, 1862, with Maj. Gen ...

under George W. Morgan from January 4, 1863 to January 12, 1863 (which was the re-designated XIII Corps (ACW)), and in the

Army of the Potomac 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 Battle of ...

and

Army of Virginia 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 ...

(see below). The first two were units of very limited life; the third was one of the most distinguished and veteran corps in the entire Union Army, commanded by very distinguished officers. The term "First Corps" is also used to describe the

First Veteran Corps The Veteran Reserve Corps (originally the Invalid Corps) was a military reserve organization created within the Union Army during the American Civil War to allow partially disabled or otherwise infirm soldiers (or former soldiers) to perform li ...

from 1864 to 1866.

History

The I Corps was created on March 3, 1862, when

President President most commonly refers to: *President (corporate title) * President (education), a leader of a college or university *President (government title) President may also refer to: Arts and entertainment Film and television *'' Præsident ...

Abraham Lincoln Abraham Lincoln (February 12, 1809 – April 15, 1865) was the 16th president of the United States, serving from 1861 until Assassination of Abraham Lincoln, his assassination in 1865. He led the United States through the American Civil War ...

ordered the creation of a five-corps

army An army, ground force or land force is an armed force that fights primarily on land. In the broadest sense, it is the land-based military branch, service branch or armed service of a nation or country. It may also include aviation assets by ...

, then under the command of Major General

George B. McClellan George Brinton McClellan (December 3, 1826 – October 29, 1885) was an American military officer and politician who served as the 24th governor of New Jersey and as Commanding General of the United States Army from November 1861 to March 186 ...

. The first commander of the corps was Major General

Irvin McDowell Irvin McDowell (October 15, 1818 – May 4, 1885) was an 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 ...

. It contained three

divisions Division may refer to: Mathematics *Division (mathematics), the inverse of multiplication * Division algorithm, a method for computing the result of mathematical division Military *Division (military), a formation typically consisting of 10,000 t ...

under the commands of Brigadier Generals William B. Franklin, George A. McCall, and

Rufus King Rufus King (March 24, 1755April 29, 1827) was an American Founding Fathers of the United States, Founding Father, lawyer, politician, and diplomat. He was a delegate from Massachusetts to the Continental Congress and the Constitutional Convent ...

. McClellan originally intended for the I Corps to participate in his

Peninsula Campaign The Peninsula campaign (also known as the Peninsular campaign) of the American Civil War was a major Union operation launched in southeastern Virginia from March to July 1862, the first large-scale offensive in the Eastern Theater. The oper ...

with the rest of the army, but after

Stonewall Jackson Thomas Jonathan "Stonewall" Jackson (January 21, 1824 – May 10, 1863) was a Confederate general and military officer who served during the American Civil War. He played a prominent role in nearly all military engagements in the eastern the ...

initiated his Valley Campaign on March 23 at the

First Battle of Kernstown The First Battle of Kernstown was fought on March 23, 1862, in Frederick County and Winchester, Virginia, the opening battle of Confederate Maj. Gen. Thomas J. "Stonewall" Jackson's campaign through the Shenandoah Valley during the American ...

, President Lincoln decided to keep the corps in northern Virginia to protect Washington. On April 4, Lincoln created the ''Department of the Rappahannock'', detaching the I Corps from the

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 The Peninsula campaign (also known as the Peninsular campaign) of the American Civil War was a major Union operation launched in southeastern Virginia from March to July 1862, the first large-scale offensive in the Eastern Theater. The oper ...

, uniting with a division of the

IV Corps 4 Corps, 4th Corps, Fourth Corps, or IV Corps may refer to: France * 4th Army Corps (France) * IV Cavalry Corps (Grande Armée), a cavalry unit of the Imperial French Army during the Napoleonic Wars * IV Corps (Grande Armée), a unit of the Imperi ...

to form the

VI Corps 6 Corps, 6th Corps, Sixth Corps, or VI Corps may refer to: France * VI Cavalry Corps (Grande Armée), a cavalry formation of the Imperial French army during the Napoleonic Wars * VI Corps (Grande Armée), a formation of the Imperial French army dur ...

. On June 18, McCall’s division, the “

Pennsylvania Reserves The Pennsylvania Reserves were an infantry division in the Union Army during the American Civil War. Noted for its famous commanders and high casualties, it served in the Eastern Theater, and fought in many important battles, including Antieta ...

”, was also detached and sent to join McClellan’s army on the

Virginia Peninsula The Virginia Peninsula is the natural landform located in southeast Virginia outlined by the York River, James River, Hampton Roads and Chesapeake Bay. It is sometimes known as the ''Lower Peninsula'' to distinguish it from two other penins ...

. Temporarily attached to the

V Corps 5th Corps, Fifth Corps, or V Corps may refer to: France * 5th Army Corps (France) * V Cavalry Corps (Grande Armée), a cavalry unit of the Imperial French Army during the Napoleonic Wars * V Corps (Grande Armée), a unit of the Imperial French Arm ...

, 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

, forming its III Corps, under the command of Irvin McDowell. 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 The Second Battle of Bull Run or Battle of Second Manassas was fought August 28–30, 1862, in Prince William County, Virginia, as part of the American Civil War. It was the culmination of the Northern Virginia Campaign waged by Confederate ...

. 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.

In early September, the I Corps, now under the command of Major General

Joseph Hooker Joseph Hooker (November 13, 1814 – October 31, 1879) 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. Hooker had serv ...

, followed Lee through Maryland and fought at South Mountain and

Antietam The Battle of Antietam ( ), also called the Battle of Sharpsburg, particularly in the Southern United States, took place during the American Civil War on September 17, 1862, between Confederate General Robert E. Lee's Army of Northern Virgin ...

. 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 George Gordon Meade (December 31, 1815 – November 6, 1872) was an American military officer who served in the United States Army and the Union army as Major General in command of the Army of the Potomac during the American Civil War from 1 ...

(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 Robert Edward Lee (January 19, 1807 – October 12, 1870) was a general officers in the Confederate States Army, Confederate general during the American Civil War, who was appointed the General in Chief of the Armies of the Confederate ...

's army at the

Battle of Fredericksburg The Battle of Fredericksburg was fought December 11–15, 1862, in and around Fredericksburg, Virginia, in the Eastern Theater of the American Civil War. The combat between the Union Army, Union Army of the Potomac commanded by Major general ( ...

, 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. John Reynolds death

In its last major battle, the

Battle of Gettysburg The Battle of Gettysburg () was a three-day battle in the American Civil War, which was fought between the Union and Confederate armies between July 1 and July 3, 1863, in and around Gettysburg, Pennsylvania. The battle, won by the Union, ...

, General Reynolds was killed just as the first troops arrived on the field, and command was inherited by Major General

Abner Doubleday Abner Doubleday (June 26, 1819 – January 26, 1893) was a career United States Army officer and Union major general in the American Civil War. He fired the first shot in defense of Fort Sumter, the opening battle of the war, and had a ...

. Although putting up a ferocious fight, the I Corps was overwhelmed by the

Confederate A confederation (also known as a confederacy or league) is a political union of sovereign states united for purposes of common action. Usually created by a treaty, confederations of states tend to be established for dealing with critical issu ...

Third Corps ( A.P. Hill) and

Robert E. Rodes Robert Emmett (or Emmet) Rodes (March 29, 1829 – September 19, 1864) was a Confederate general in the American Civil War, and the first of Robert E. Lee's divisional commanders not trained at West Point. His division led Stonewall Jackson ...

'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 Cemetery Hill is a landform on the Gettysburg Battlefield that was the scene of fighting each day of the Battle of Gettysburg (July 1–3, 1863). The northernmost part of the Army of the Potomac defensive " fish-hook" line, the hill is gent ...

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 John Newton (; – 21 December 1807) was an English evangelical Anglican cleric and slavery Abolitionism, abolitionist. He had previously been a captain of slave ships and an investor in the slave trade. He served as a sailor in the Royal Nav ...

, a division commander from the

. 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 Pickett's Charge was an infantry assault on July 3, 1863, during the Battle of Gettysburg. It was ordered by Confederate General Robert E. Lee as part of his plan to break through Union lines and achieve a decisive victory in the North. T ...

, and through the

Mine Run Campaign The Battle of Mine Run, also known as Payne's Farm, or New Hope Church, or the Mine Run campaign (November 27 – December 2, 1863), was conducted in Orange County, Virginia, in the American Civil War. An unsuccessful attempt of the Union ...

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

of the Army of the Potomac.

Command history

* As III Corps,

References

*Eicher, John H., & Eicher, David J.: ''Civil War High Commands'', Stanford University Press, 2001, *Fox, William F.: ''Regimental Losses in the American Civil War'', Albany Publishing, 1889
online text of I Corps section
*Wipperman, Darin: ''First for the Union: Life and Death in a Civil War Army Corps from Antietam to Gettysburg'', Stackpole, 2020 {{Gettysburg Campaign 01 Military units and formations established in 1862 1862 establishments in the United States Military units and formations disestablished in 1864