XXI Corps was a 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...

 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...

. It served as part of William S. Rosecrans's 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:...

 and was in existence from January 9th to October 1863.

After the Battle of Stone's River, General Rosecrans reorganized the "wings" of his army into three corps. The left wing, under Thomas L. Crittenden, became the XXI Corps.

Taking part in the Tullahoma Campaign

Tullahoma Campaign

The Tullahoma Campaign or Middle Tennessee Campaign was fought between June 24 and July 3, 1863, during the American Civil War. The Union Army of the Cumberland, commanded by Maj. Gen. William S...

, the XXI Corps was heavily engaged 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...

 on September 19-20, 1863, where it was nearly destroyed. It was Rosecrans' mistaken decision to pull Thomas 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:...

's division of this corps to support George 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....

's XIV Corps

XIV Corps (ACW)

XIV Corps was a corps of the Union Army during the American Civil War. It was one of the earliest corps formations in the Western Theater of the American Civil War.-Creation:...

 that resulted in General James Longstreet

James Longstreet

James Longstreet 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 commander for many of the famous battles fought by the Army of Northern Virginia in the...

's breakthrough against the Union center. It should be added, though, that elements of XXI Corps, most notably William J. Palmer's division, aided Thomas in his successful rearguard action on Snodgrass Hill. Along with the remnants of XX Corps

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 :...

, the corps reorganized into IV Corps

IV Corps (ACW)

There were two corps of the Union Army called IV Corps during the American Civil War. They were separate units, one serving with the Army of the Potomac and the Department of Virginia in the Eastern Theater, 1862–63, the other with the Army of the Cumberland in the Western Theater,...

shortly after the battle.

External links

• XXI Corps history