Two

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 first named as such in 1805. The size of a corps varies great ...

of the

Union Army During the American Civil War, the Union Army, also known as the Federal Army and the Northern Army, referring to the United States Army, was the land force that fought to preserve the Union (American Civil War), Union of the collective U.S. st ...

were called XX Corps during the

American Civil War The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...

. Though both served in the Union

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 creation ...

, they were distinct units and should be recognized as such.

McCook's Corps

The first XX Corps, under the command of Alexander M. McCook, was organized in the aftermath of the

Battle of Stones River The Battle of Stones River, also known as the Second Battle of Murfreesboro, was a battle fought from December 31, 1862, to January 2, 1863, in Middle Tennessee, as the culmination of the Stones River Campaign in the Western Theater of the Ame ...

in January 1863 from what had been the

XIV Corps 14 Corps, 14th Corps, Fourteenth Corps, or XIV Corps may refer to: * XIV Corps (Grande Armée), a unit of the Imperial French Army during the Napoleonic Wars * XIV Corps (German Empire), a unit of the Imperial German Army prior to and during World ...

, or right wing of the army, at that battle. It was so identified with its commander that it was generally referred to by other soldiers and even officers as "McCook's corps". The corps took part in a skirmish with Bragg's rearguard at Liberty Gap, Tennessee, during the Tullahoma Campaign in June 1863. It fought its only major battle under this designation at

Chickamauga Chickamauga may refer to: Entertainment * "Chickamauga", an 1889 short story by American author Ambrose Bierce * "Chickamauga", a 1937 short story by Thomas Wolfe * "Chickamauga", a song by Uncle Tupelo from their 1993 album ''Anodyne'' * ''Chic ...

, where it suffered horrendous casualties in the two days of fighting. The corps took heavy casualties, and it (along with

Thomas L. Crittenden Thomas Leonidas Crittenden (May 15, 1819 – October 23, 1893) was a lawyer, politician, and Union general during the American Civil War. Early life Crittenden was born in Russellville, Kentucky, the son of U.S. Senator John J. Crittenden, who ...

's XXI Corps), became consolidated into the new IV Corps. McCook, blamed in large part for the failure at Chickamauga, was relieved of command.

Command history

* Alexander M. McCook, January 9, 1863 – October 9, 1863

Hooker's corps

After the

Battle of Gettysburg The Battle of Gettysburg () was fought July 1–3, 1863, in and around the town of Gettysburg, Pennsylvania, by Union and Confederate forces during the American Civil War. In the battle, Union Major General George Meade's Army of the Po ...

, with the armies of the east engaged in stalemate (and a large portion of Robert E. Lee's

Army of Northern Virginia 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 oft ...

, under

James Longstreet James Longstreet (January 8, 1821January 2, 1904) was one of the foremost Confederate generals of the American Civil War and the principal subordinate to General Robert E. Lee, who called him his "Old War Horse". He served under Lee as a corps ...

, was serving with

Braxton Bragg Braxton Bragg (March 22, 1817 – September 27, 1876) was an American army officer during the Second Seminole War and Mexican–American War and Confederate general in the Confederate Army during the American Civil War, serving in the Weste ...

in Tennessee), Washington dispatched

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 ...

, discredited after his defeat at the

Battle of Chancellorsville The Battle of Chancellorsville, April 30 – May 6, 1863, was a major battle of the American Civil War (1861–1865), and the principal engagement of the Chancellorsville campaign. Chancellorsville is known as Lee's "perfect battle" because h ...

the previous May, with the XI and

XII Corps 12th Corps, Twelfth Corps, or XII Corps may refer to: * 12th Army Corps (France) * XII Corps (Grande Armée), a corps of the Imperial French Army during the Napoleonic Wars * XII (1st Royal Saxon) Corps, a unit of the Imperial German Army * XII ...

of the

Army of the Potomac 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 Confedera ...

to try to relieve Bragg's siege of Chattanooga. The command played a decisive role in the

Battle of Wauhatchie The Battle of Wauhatchie was fought October 28–29, 1863, in Hamilton and Marion counties, Tennessee, and Dade County, Georgia, in the American Civil War. A Union force had seized Brown's Ferry on the Tennessee River, opening a supply line ...

, which opened up the "Cracker Line" to the besieged Union army, and seized

Lookout Mountain Lookout Mountain is a mountain ridge located at the northwest corner of the U.S. state of Georgia, the northeast corner of Alabama, and along the southeastern Tennessee state line in Chattanooga. Lookout Mountain was the scene of the 18th-cen ...

in the famed "Battle Above The Clouds" during the early stages of the Battle of Chattanooga. On April 4, 1864, just before the onset of the Atlanta Campaign,

William T. Sherman William is a male given name of Germanic origin.Hanks, Hardcastle and Hodges, ''Oxford Dictionary of First Names'', Oxford University Press, 2nd edition, , p. 276. It became very popular in the English language after the Norman conquest of Engl ...

, authorized the consolidation of XI and XII Corps as XX Corps, under Hooker's command, to serve in the

. Units from XI and XII Corps were combined in each division. The corps fought valiantly throughout the Atlanta Campaign. After

James B. McPherson James Birdseye McPherson (November 14, 1828 – July 22, 1864) was a career United States Army officer who served as a general in the Union Army during the American Civil War. McPherson was on the General's staff of Henry Halleck and late ...

was killed in the

Battle of Atlanta The Battle of Atlanta was a battle of the Atlanta Campaign fought during the American Civil War on July 22, 1864, just southeast of Atlanta, Georgia. Continuing their summer campaign to seize the important rail and supply hub of Atlanta, Uni ...

on July 22, Oliver O. Howard was made commander of the

Army of the Tennessee An army (from Old French ''armee'', itself derived from the Latin verb ''armāre'', meaning "to arm", and related to the Latin noun ''arma'', meaning "arms" or "weapons"), ground force or land force is a fighting force that fights primarily on ...

. Hooker, partially because Howard was junior to him and partially because he blamed Howard (who had commanded

XI Corps 11 Corps, 11th Corps, Eleventh Corps, or XI Corps may refer to: * 11th Army Corps (France) * XI Corps (Grande Armée), a unit of the Imperial French Army during the Napoleonic Wars * XI Corps (German Empire), a unit of the Imperial German Army * ...

at the

, where it had been routed during

Stonewall Jackson Thomas Jonathan "Stonewall" Jackson (January 21, 1824 – May 10, 1863) was a Confederate general during the American Civil War, considered one of the best-known Confederate commanders, after Robert E. Lee. He played a prominent role in nearl ...

's famed flank march) for his part in the defeat of the

, resigned. He was replaced first by

Alpheus S. Williams Alpheus Starkey Williams (September 20, 1810 – December 21, 1878) was a lawyer, judge, journalist, U.S. Congressman, and a Union Army, Union general in the American Civil War. Early life Williams was born in Deep River, Connecticut. He gradua ...

, and then Henry W. Slocum, both former

commanders. Its troops were the first to enter Atlanta after its surrender on September 1, and later went with Sherman's

Army of Georgia The Army of Georgia was a Union army that constituted the Left Wing of Major General William T. Sherman's Army Group during the March to the Sea and the Carolinas Campaign. History During Sherman's Atlanta Campaign in 1864, his Army Group wa ...

during his March to the Sea. Williams commanded it from then until the

Carolinas Campaign The campaign of the Carolinas (January 1 – April 26, 1865), also known as the Carolinas campaign, was the final campaign conducted by the United States Army (Union Army) against the Confederate States Army in the Western Theater. On January 1 ...

(Slocum having been promoted to army command in the meantime). It played a major part in the seizure of Savannah in December and was actively engaged throughout the Carolinas Campaign, particularly at Bentonville, where it absorbed the main blow of

Joseph E. Johnston Joseph Eggleston Johnston (February 3, 1807 – March 21, 1891) was an American career army officer, serving with distinction in the United States Army during the Mexican–American War (1846–1848) and the Seminole Wars. After Virginia secede ...

's counterattack. Because fighting at Bentonville had not destroyed Johnston's army, Sherman replaced Williams with the more aggressive

Joseph A. Mower Joseph Anthony Mower (August 22, 1827 – January 6, 1870) was a Union general during the American Civil War. He was a competent officer and well respected by his troops and fellow officers to whom he was known as "Fighting Joe". Major General Wil ...

. It took part in the Grand Review and was disbanded in June 1865.

Command history

, April 14, 1864 – July 28, 1864 *

, July 28, 1864 – August 27, 1864 * Henry W. Slocum, August 27, 1864 – November 11, 1864 *

, November 11, 1864 – April 2, 1865 *

, April 2, 1865 – June 4, 1865

External links

(McCook's) XX Corps historyRoute of the Twentieth Corps
historical marker {{Union Army Formations 20 Military units and formations established in 1863 1863 establishments in the United States Military units and formations disestablished in 1865