There were two 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...

 of 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...

 called IV Corps 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...

. They were separate units, one serving with 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...

 and the Department of Virginia in the Eastern Theater, 1862–63, the other with the 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:...

 in the Western Theater, 1863–65.

IV Corps (Eastern Theater)

The IV Corps, Army of the Potomac, was created on March 13, 1862, and placed under the command of Erasmus D. Keyes

Erasmus D. Keyes

Erasmus Darwin Keyes was a businessman, banker, and military general, noted for leading the IV Corps of the Union Army of the Potomac during the first half of the American Civil War.-Early life and career:...

, who had commanded a brigade at First Bull Run

First Battle of Bull Run

First Battle of Bull Run, also known as First Manassas , was fought on July 21, 1861, in Prince William County, Virginia, near the City of Manassas...

. It consisted initially of three divisions, under Darius N. Couch

Darius N. Couch

Darius Nash Couch was an American soldier, businessman, and naturalist. He served as a career U.S. Army officer during the Mexican-American War, the Second Seminole War, and as a general officer in the Union Army during the American Civil War.During the Civil War, Couch fought notably in the...

, Silas Casey

Silas Casey

Silas Casey was a career United States Army officer who rose to the rank of Major General during the American Civil War.-Early life and military career:...

, and William F. “Baldy” Smith

William Farrar Smith

William Farrar Smith , was a civil engineer, a member of the New York City police commission, and Union general in the American Civil War.-Early life:...

. Couch's division was transferred to join 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...

 during the Antietam Campaign and remained with them for the duration of the war. The corps' peak strength (in early 1862) was 37,000 men.
The corps took part in 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...

's 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...

 of 1862, playing a major role in repulsing Confederate attacks at Seven Pines

Battle of Seven Pines

The Battle of Seven Pines, also known as the Battle of Fair Oaks or Fair Oaks Station, took place on May 31 and June 1, 1862, in Henrico County, Virginia, as part of the Peninsula Campaign of the American Civil War. It was the culmination of an offensive up the Virginia Peninsula by Union Maj. Gen....

 and Malvern Hill

Battle of Malvern Hill

The Battle of Malvern Hill, also known as the Battle of Poindexter's Farm, took place on July 1, 1862, in Henrico County, Virginia, on the seventh and last day of the Seven Days Battles of the American Civil War. Gen. Robert E. Lee launched a series of disjointed assaults on the nearly impregnable...

. After the campaign, IV Corps remained on the Peninsula

Virginia Peninsula

The Virginia Peninsula is a peninsula in southeast Virginia, USA, bounded by the York River, James River, Hampton Roads and Chesapeake Bay.Hampton Roads is the common name for the metropolitan area that surrounds the body of water of the same name...

, with Couch's division later detached. The corps was attached to the Department of Virginia under John A. Dix

John Adams Dix

John Adams Dix was an American politician from New York. He served as Secretary of the Treasury, U.S. Senator, and the 24th Governor of New York. He was also a Union major general during the Civil War.-Early life and career:...

, and took part (along with VII Corps

VII Corps (ACW)

Two corps of the Union Army were called VII Corps during the American Civil War.-VII Corps :This corps was established 22 July 1862 from various Union troops stationed in southeastern Virginia. The corps' main combat action occurred in the spring of 1863, when it faced Confederate troops of James...

) in minor diversionary actions against Richmond during the Gettysburg Campaign

Gettysburg Campaign

The Gettysburg Campaign was a series of battles fought in June and July 1863, during the American Civil War. After his victory in the Battle of Chancellorsville, Confederate General Robert E. Lee's Army of Northern Virginia moved north for offensive operations in Maryland and Pennsylvania. The...

. The corps was officially discontinued on August 1, 1863.

Command History

Erasmus D. Keyes Erasmus D. Keyes Erasmus Darwin Keyes was a businessman, banker, and military general, noted for leading the IV Corps of the Union Army of the Potomac during the first half of the American Civil War.-Early life and career:...	March 13, 1862 – August, 1862	Army of the Potomac
Erasmus D. Keyes Erasmus D. Keyes Erasmus Darwin Keyes was a businessman, banker, and military general, noted for leading the IV Corps of the Union Army of the Potomac during the first half of the American Civil War.-Early life and career:...	August, 1862 – August 1, 1863	Department of Virginia

IV Corps (Western Theater)

This corps was created on October 10, 1863, from the remnants of XX

XX Corps (ACW)

Two corps of the Union Army were called XX Corps during the American Civil War. Though both served in the Union Army of the Cumberland, they were distinct units and should be recognized as such.- McCook's Corps :...

 and XXI Corps

XXI Corps (ACW)

XXI Corps was a corps of the Union Army during the American Civil War. It served as part of William S. Rosecrans's Army of the Cumberland and was in existence from January 9th to October 1863....

, both of which had suffered heavy casualties at Chickamauga

Battle of Chickamauga

The Battle of Chickamauga, fought September 19–20, 1863, marked the end of a Union offensive in southeastern Tennessee and northwestern Georgia called the Chickamauga Campaign...

. It was initially commanded by Gordon Granger

Gordon Granger

Gordon Granger was a career U.S. army officer and a Union general during the American Civil War. He distinguished himself at the Battle of Chickamauga.-Early life & Mexico:...

 and its division commanders were Philip Sheridan

Philip Sheridan

Philip Henry Sheridan was a career United States Army officer and a Union general in the American Civil War. His career was noted for his rapid rise to major general and his close association with Lt. Gen. Ulysses S...

, John Palmer

John M. Palmer (politician)

John McAuley Palmer , was an Illinois resident, an American Civil War General who fought for the Union, the 15th Governor of Illinois, and presidential candidate of the National Democratic Party in the 1896 election on a platform to defend the gold standard, free trade, and limited...

, and Thomas J. Wood

Thomas J. Wood

Thomas John Wood was a career United States Army officer and a Union general during the American Civil War.-Early life and career:...

. It served with distinction in the famous unordered attack on Missionary Ridge

Missionary Ridge

Missionary Ridge is a geographic feature in Chattanooga, Tennessee, site of the Battle of Missionary Ridge, a battle in the American Civil War, fought on November 25, 1863. Union forces under Maj. Gens. Ulysses S. Grant, William T. Sherman, and George H...

 at Chattanooga, and served in the Knoxville

Knoxville Campaign

The Knoxville Campaign was a series of American Civil War battles and maneuvers in East Tennessee during the fall of 1863. Union forces under Maj. Gen. Ambrose Burnside occupied Knoxville, Tennessee, and Confederate forces under Lt. Gen. James Longstreet were detached from Gen...

 and Atlanta

Atlanta Campaign

The Atlanta Campaign was a series of battles fought in the Western Theater of the American Civil War throughout northwest Georgia and the area around Atlanta during the summer of 1864. Union Maj. Gen. William T. Sherman invaded Georgia from the vicinity of Chattanooga, Tennessee, beginning in May...

 Campaigns. During John B. Hood's Franklin-Nashville Campaign

Franklin-Nashville Campaign

The Franklin-Nashville Campaign, also known as Hood's Tennessee Campaign, was a series of battles in the Western Theater, conducted from September 18 to December 27, 1864, in Alabama, Tennessee, and northwestern Georgia during the American Civil War. The Confederate Army of Tennessee under Lt....

, General William T. Sherman left the IV (and XXIII Corps

XXIII Corps (ACW)

XXIII Corps was a corps of the Union Army during the American Civil War. It served in the Western Theater as part of the Army of the Ohio.The corps was organized in April 1863 by order of the departmental commander, Ambrose E. Burnside...

), under the overall command of General George H. Thomas

George Henry Thomas

George Henry Thomas was a career United States Army officer and a Union General during the American Civil War, one of the principal commanders in the Western Theater....

, to defend Tennessee, and the corps was heavily engaged in the battles at Spring Hill

Battle of Spring Hill

The Battle of Spring Hill was fought November 29, 1864, at Spring Hill, Tennessee, as part of the Franklin-Nashville Campaign of the American Civil War. The Confederate Army of Tennessee, commanded by Lt. Gen. John Bell Hood, attacked a Union force under Maj. Gen. John M. Schofield as it...

, Franklin

Battle of Franklin

Battle of Franklin may refer to three battles of the American Civil War:* Battle of Franklin , a major battle fought November 30, 1864, at Franklin, Tennessee as part of the Franklin-Nashville Campaign...

, and Nashville

Battle of Nashville

The Battle of Nashville was a two-day battle in the Franklin-Nashville Campaign that represented the end of large-scale fighting in the Western Theater of the American Civil War. It was fought at Nashville, Tennessee, on December 15–16, 1864, between the Confederate Army of Tennessee under...

. When the force Thomas commanded at Nashville was divided, he was left in command only of the IV Corps and cavalry under James H. Wilson

James H. Wilson

James Harrison Wilson was a United States Army topographic engineer, a Union Army Major General in the American Civil War and later wars, a railroad executive, and author.-Early life and engineering:...

 and George Stoneman

George Stoneman

George Stoneman, Jr. was a career United States Army officer, a Union cavalry general in the American Civil War, and the 15th Governor of California between 1883 and 1887.-Early life:...

. The IV Corps was ordered to block the mountain passes and prevent a potential retreat by Lee's army into the mountains.

Records differ regarding the further history of the corps. Two sources report that it was deactivated on August 1, 1865. A third reports that after the war it was sent to Texas as part of the U.S. Army detachment dispatched to persuade French Emperor Napoleon III

Napoleon III of France

Louis-Napoléon Bonaparte was the President of the French Second Republic and as Napoleon III, the ruler of the Second French Empire. He was the nephew and heir of Napoleon I, christened as Charles Louis Napoléon Bonaparte...

 to withdraw his troops from Mexico, and was not disbanded until December 1865.

Command History

Gordon Granger Gordon Granger Gordon Granger was a career U.S. army officer and a Union general during the American Civil War. He distinguished himself at the Battle of Chickamauga.-Early life & Mexico:...	October 10, 1863 – April 10, 1864	Chattanooga and Knoxville
Oliver O. Howard Oliver O. Howard Oliver Otis Howard was a career United States Army officer and a Union general in the American Civil War...	April 10, 1864 – July 27, 1864	to Atlanta
David S. Stanley David S. Stanley David Sloane Stanley was a Union Army officer during the American Civil War and a recipient of America's highest military decoration, the Medal of Honor, for his actions at the Battle of Franklin.-Early life:...	July 27, 1864 – December 1, 1864	wounded at Franklin
Thomas J. Wood Thomas J. Wood Thomas John Wood was a career United States Army officer and a Union general during the American Civil War.-Early life and career:...	December 1, 1864 – January 31, 1865	Nashville
David S. Stanley David S. Stanley David Sloane Stanley was a Union Army officer during the American Civil War and a recipient of America's highest military decoration, the Medal of Honor, for his actions at the Battle of Franklin.-Early life:...	January 31, 1865 – August 1, 1865