I Corps was the designation of three different corps

Corps

A corps is either a large formation, or an administrative grouping of troops within an armed force with a common function such as Artillery or Signals representing an arm of service...

-sized units in the Union Army

Union Army

The Union Army was the land force that fought for the Union during the American Civil War. It was also known as the Federal Army, the U.S. Army, the Northern Army and the National Army...

 during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

. The units served in the following armies:

• Army of the Ohio
  Army of the Ohio
  The Army of the Ohio was the name of two 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:...
  
  /Army of the Cumberland
  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:...
  
  , Alexander M. McCook, September 29, 1862 – November 5, 1862
• Army of the Mississippi
  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.-1862:...
  
  , George W. Morgan
  George W. Morgan
  George Washington Morgan was an American soldier, lawyer, politician, and diplomat. He fought in the Texas Revolution and the Mexican-American War, and was a general in the Union Army during the American Civil War...
  
  , January 4, 1863 – January 12, 1863
• Army of the Potomac
  Army of the Potomac
  The Army of the Potomac was the major Union Army in the Eastern Theater of the American Civil War.-History:The Army of the Potomac was created in 1861, but was then only the size of a corps . Its nucleus was called the Army of Northeastern Virginia, under Brig. Gen...
  
   and Army of Virginia
  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, commanded by Robert E...
  
   (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.

History

The I Corps was activated March 13, 1862, when President

President of the United States

The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 Abraham Lincoln

Abraham Lincoln

Abraham Lincoln was the 16th President of the United States, serving from March 1861 until his assassination in April 1865. He successfully led his country through a great constitutional, military and moral crisis – the American Civil War – preserving the Union, while ending slavery, and...

 ordered the creation of a four-corps army, then under the command of Major General George B. McClellan

George B. McClellan

George Brinton McClellan was a major general during the American Civil War. He organized the famous Army of the Potomac and served briefly as the general-in-chief of the Union Army. Early in the war, McClellan played an important role in raising a well-trained and organized army for the Union...

. The first commander of this corps was Major General

Major General

Major general or major-general is a military rank used in many countries. It is derived from the older rank of sergeant major general. A major general is a high-ranking officer, normally subordinate to the rank of lieutenant general and senior to the ranks of brigadier and brigadier general...

 Irvin McDowell

Irvin McDowell

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.-Early life:...

 and it contained three divisions

Division (military)

A division is a large military unit or formation usually consisting of between 10,000 and 20,000 soldiers. In most armies, a division is composed of several regiments or brigades, and in turn several divisions typically make up a corps...

. It was held in defense of Washington while the rest of the Army of the Potomac

Army of the Potomac

The Army of the Potomac was the major Union Army in the Eastern Theater of the American Civil War.-History:The Army of the Potomac was created in 1861, but was then only the size of a corps . Its nucleus was called the Army of Northeastern Virginia, under Brig. Gen...

 advanced to the Peninsula Campaign

Peninsula Campaign

The Peninsula Campaign of the American Civil War was a major Union operation launched in southeastern Virginia from March through July 1862, the first large-scale offensive in the Eastern Theater. The operation, commanded by Maj. Gen. George B...

.

It was then consolidated into the Army of Virginia

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, commanded by Robert E...

 under Major General John Pope

John Pope (military officer)

John Pope was a career United States Army officer and Union general in the American Civil War. He had a brief but successful career in the Western Theater, but he is best known for his defeat at the Second Battle of Bull Run in the East.Pope was a graduate of the United States Military Academy in...

, and fought in the Second Battle of Bull Run

Second Battle of Bull Run

The Second Battle of Bull Run or Second Manassas was fought August 28–30, 1862, as part of the American Civil War. It was the culmination of an offensive campaign waged by Confederate Gen. Robert E. Lee's Army of Northern Virginia against Union Maj. Gen...

, as the Third Corps, Army of Virginia

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, commanded by Robert E...

. Afterwards, its name was restored. It rejoined the Army of the Potomac and crossed the Potomac River

Potomac River

The Potomac River flows into the Chesapeake Bay, located along the mid-Atlantic coast of the United States. The river is approximately long, with a drainage area of about 14,700 square miles...

 into Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

 to fight in the Battle of Antietam

Battle of Antietam

The Battle of Antietam , fought on September 17, 1862, near Sharpsburg, Maryland, and Antietam Creek, as part of the Maryland Campaign, was the first major battle in the American Civil War to take place on Northern soil. It was the bloodiest single-day battle in American history, with about 23,000...

, under Major General Joseph Hooker

Joseph Hooker

Joseph Hooker was a career United States Army officer, achieving the rank of major general in the Union Army during the American Civil War. Although he served throughout the war, usually with distinction, Hooker is best remembered for his stunning defeat by Confederate General Robert E...

. There, the division of Pennsylvania Reserves

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 Antietam and Gettysburg....

, under Brigadier General

Brigadier General

Brigadier general is a senior rank in the armed forces. It is the lowest ranking general officer in some countries, usually sitting between the ranks of colonel and major general. When appointed to a field command, a brigadier general is typically in command of a brigade consisting of around 4,000...

 George G. Meade, took heavy casualties through its hard fighting, and was withdrawn to replenish.

The corps moved southward to fight General Robert E. Lee

Robert E. Lee

Robert Edward Lee was a career military officer who is best known for having commanded the Confederate Army of Northern Virginia in the American Civil War....

's army at the Battle of Fredericksburg

Battle of Fredericksburg

The Battle of Fredericksburg was fought December 11–15, 1862, in and around Fredericksburg, Virginia, between General Robert E. Lee's Confederate Army of Northern Virginia and the Union Army of the Potomac, commanded by Maj. Gen. Ambrose E. Burnside...

, commanded by Major General John F. Reynolds

John F. Reynolds

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.-Early...

, arguably the best Union corps commander in the Eastern Theater. He superbly led the corps through this battle, then through the Battle of Chancellorsville

Battle of Chancellorsville

The Battle of Chancellorsville was a major battle of the American Civil War, and the principal engagement of the Chancellorsville Campaign. It was fought from April 30 to May 6, 1863, in Spotsylvania County, Virginia, near the village of Chancellorsville. Two related battles were fought nearby on...

, where the I Corps was left in reserve.
In its last major battle, the Battle of Gettysburg

Battle of Gettysburg

The Battle of Gettysburg , was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania. The battle with the largest number of casualties in the American Civil War, it is often described as the war's turning point. Union Maj. Gen. George Gordon Meade's Army of the Potomac...

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

Abner Doubleday

Abner Doubleday was a career United States Army officer and Union 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 pivotal role in the early fighting at the Battle of Gettysburg. Gettysburg was his finest hour, but his...

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

Confederate States of America

The Confederate States of America was a government set up from 1861 to 1865 by 11 Southern slave states of the United States of America that had declared their secession from the U.S...

 Third Corps (A.P. Hill) and Robert E. Rodes

Robert E. Rodes

Robert Emmett Rodes was a railroad civil engineer and a promising young Confederate general in the American Civil War, killed in battle in the Shenandoah Valley.-Education, antebellum career:...

's division of Richard S. Ewell

Richard S. Ewell

Richard Stoddert Ewell was a career United States Army officer and a Confederate general during the American Civil War. He achieved fame as a senior commander under Stonewall Jackson and Robert E...

's Second Corps. It was forced to retreat through the town of Gettysburg, taking up defensive positions on Cemetery Hill

Cemetery Hill

Cemetery Hill is a Gettysburg Battlefield landform which had 1863 military engagements each day of the July 1–3 Battle of Gettysburg. The northernmost part of the Army of the Potomac defensive "fish-hook" line, the hill is gently sloped and provided a site for American Civil War artillery...

. The next day (July 2, 1863), the command was given to Major General John Newton, a division commander from the VI Corps

VI Corps (ACW)

The VI Corps was a corps of the Union Army during the American Civil War.-Formation:The corps was organized as the Sixth Provisional Corps on May 18, 1862, by uniting Maj. Gen. William B. Franklin's Division, which had just arrived on the Virginia Peninsula, with Maj. Gen. William F. Smith's...

. 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

Pickett's Charge was an infantry assault ordered by Confederate Gen. Robert E. Lee against Maj. Gen. George G. Meade's Union positions on Cemetery Ridge on July 3, 1863, the last day of the Battle of Gettysburg during the American Civil War. Its futility was predicted by the charge's commander,...

, 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

V Corps (ACW)

The V Corps was a unit of the Union Army of the Potomac during the American Civil War.-1862:The corps was first organized briefly under Nathaniel P. Banks, but then permanently on May 18, 1862, designated as the "V Corps Provisional"...

 of the Army of the Potomac.

Command history

Irvin McDowell Irvin McDowell 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.-Early life:...	March 13, 1862 – April 4, 1862
Irvin McDowell Irvin McDowell 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.-Early life:... *	June 26, 1862 – September 5, 1862
James B. Ricketts James B. Ricketts James Brewerton Ricketts was a career officer in the United States Army, serving as a Union Army general in the Eastern Theater during the American Civil War.-Early life and career:... *	September 5, 1862 – September 6, 1862
Joseph Hooker Joseph Hooker Joseph Hooker was a career United States Army officer, achieving the rank of major general in the Union Army during the American Civil War. Although he served throughout the war, usually with distinction, Hooker is best remembered for his stunning defeat by Confederate General Robert E... *	September 6, 1862 – September 12, 1862
Joseph Hooker Joseph Hooker Joseph Hooker was a career United States Army officer, achieving the rank of major general in the Union Army during the American Civil War. Although he served throughout the war, usually with distinction, Hooker is best remembered for his stunning defeat by Confederate General Robert E...	September 12, 1862 – September 17, 1862
George G. Meade	September 17, 1862 – September 29, 1862
John F. Reynolds John F. Reynolds 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.-Early...	September 29, 1862 – January 2, 1863
James S. Wadsworth James S. Wadsworth James Samuel Wadsworth was a philanthropist, politician, and a Union general in the American Civil War. He was killed in battle during the Battle of the Wilderness of 1864.-Early years:...	January 2, 1863 – January 4, 1863
John F. Reynolds John F. Reynolds 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.-Early...	January 4, 1863 – March 1, 1863
James S. Wadsworth James S. Wadsworth James Samuel Wadsworth was a philanthropist, politician, and a Union general in the American Civil War. He was killed in battle during the Battle of the Wilderness of 1864.-Early years:...	March 1, 1863 – March 9, 1863
John F. Reynolds John F. Reynolds 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.-Early...	March 9, 1863 – July 1, 1863
Abner Doubleday Abner Doubleday Abner Doubleday was a career United States Army officer and Union 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 pivotal role in the early fighting at the Battle of Gettysburg. Gettysburg was his finest hour, but his...	July 1, 1863 – July 2, 1863
John Newton	July 2, 1863 – March 12, 1864
James S. Wadsworth James S. Wadsworth James Samuel Wadsworth was a philanthropist, politician, and a Union general in the American Civil War. He was killed in battle during the Battle of the Wilderness of 1864.-Early years:...	March 12, 1864 – March 14, 1864
John Newton	March 14, 1864 – March 24, 1864

* As III Corps, Army of Virginia

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, commanded by Robert E...