XX Corps (Union Army)

XX Corps (Union Army)
Public domain · source
Unit name	XX Corps
Caption	Flag of the XX Corps
Dates	1863–1865
Country	United States (Union)
Allegiance	Union
Branch	Army
Type	Corps
Size	Corps
Notable commanders	William T. Sherman, Joseph Hooker

XX Corps (Union Army) was a corps-level formation of the Union Army during the American Civil War created in the Western Theater and later active in the Atlanta Campaign, March to the Sea, and Carolinas Campaign. Organized from veterans of prior formations, it served under prominent leaders and participated in major actions that shaped the campaigns of William T. Sherman and operational efforts against the Confederate States Army of Joseph E. Johnston and John Bell Hood. The corps earned recognition for its role in maneuver warfare, siege operations, and coordinated corps-level assaults.

Formation and Organization

The XX Corps was formed in April 1864 by consolidating elements of the XIV Corps (Union Army) and the XXI Corps (Union Army) under the Army of the Cumberland and the Army of the Tennessee reorganization that preceded the Atlanta Campaign. The creation followed strategic directives from Ulysses S. Grant and operational planning by Henry W. Halleck to concentrate forces for the offensive against Atlanta. The corps integrated divisions previously commanded by officers drawn from Ohio volunteer regiments, Illinois Volunteer Infantry, Indiana Volunteers, and Pennsylvania Volunteers, reflecting troop distributions from the Western Theater of the American Civil War.

Commanders and Staff

Initial command of the XX Corps was given to William T. Sherman's subordinate corps commanders and for a time exercised by Joseph Hooker after he was reassigned west from the Army of the Potomac. Other senior figures associated with the corps included George H. Thomas, who coordinated adjacent forces, and division commanders such as John W. Geary and Joseph A. Mower. Staff officers and brigade leaders included veterans from the Army of the Cumberland staff cadre and aides who had served under Don Carlos Buell and Ambrose Burnside. The corps’ staff worked closely with the headquarters of the Military Division of the Mississippi to synchronize logistics, reconnaissance, and artillery support during combined operations with the XV Corps (Union Army) and XVII Corps (Union Army).

Military Engagements and Campaigns

The XX Corps saw sustained combat in the Atlanta Campaign from May to September 1864, engaging in operations at Kennesaw Mountain, the battles around Marietta, and the flanking movements that forced the evacuation of Atlanta. During the Siege of Atlanta, elements of the corps participated in assaults, siege works, and entrenchment against Confederate forces under John Bell Hood. After Atlanta fell, the corps joined Sherman’s March to the Sea, conducting destructive maneuver warfare across Georgia and demonstrating coordinated foraging, railroad disruption, and skirmishing. In the Carolinas Campaign, the XX Corps fought in operations culminating in the surrender negotiations with Robert E. Lee’s contemporaries and the eventual surrender of Confederate forces led by Joseph E. Johnston at Bennett Place. Notable actions also included engagements at Resaca, New Hope Church, and crossings of the Chattahoochee River and Savannah approaches. The corps’ actions influenced strategic outcomes in the Atlanta Campaign, Savannah campaign, and the campaign that led to the capitulation of major Confederate field armies.

Order of Battle and Unit Composition

The XX Corps order of battle comprised multiple divisions, brigades, regiments, and attached artillery batteries drawn primarily from volunteer infantry regiments of Ohio, Indiana, Illinois, Pennsylvania, New York, and Michigan. Regiments such as the 20th Ohio Volunteer Infantry Regiment, 27th Indiana Volunteer Infantry Regiment, and 24th Michigan Volunteer Infantry Regiment served within its brigades at various times, alongside veteran Zouave and sharpshooter companies transferred from earlier corps. Artillery support was provided by batteries formerly of the Army of the Tennessee artillery reserve and light artillery sections familiar from engagements under William S. Rosecrans and George B. McClellan’s predecessor formations. Cavalry detachments coordinating with the corps included scouts and screening elements from divisions once attached to the Cavalry Corps, Army of the Potomac and western cavalry units that supported reconnaissance and raiding operations during the March to the Sea.

Casualties and Losses

Throughout its campaigns from 1864 to 1865, the XX Corps sustained significant casualties from combat, disease, and attrition during long marches and siege operations. Major engagements such as Kennesaw Mountain and the assaults during the Siege of Atlanta accounted for hundreds of killed and wounded among infantry regiments, while deadly outbreaks of disease mirrored patterns seen across the Civil War hospital system and led to additional non-combat losses. The corps also reported men captured during skirmishes and detachments lost during raids and foraging expeditions. Aggregate casualty figures are reflected in regimental returns submitted to the War Department (United States) and compiled in postwar muster rolls and veterans’ reports.

Postwar Demobilization and Legacy

After Appomattox and the surrender of major Confederate forces, XX Corps units participated in occupation duties and the demobilization process ordered by the United States War Department and conducted in coordination with William T. Sherman’s headquarters. Veterans returned to states such as Ohio, Indiana, Illinois, and Pennsylvania, where they formed Grand Army of the Republic posts, participated in veterans' reunions, and contributed to memorialization through monuments at battlefields like Kennesaw Mountain National Battlefield Park and Savannah National Historic Landmark District. The corps’ campaigns influenced postwar military thinking on combined arms operations, logistics, and maneuver, and its legacy is reflected in regimental histories, battlefield commemorations, and scholarship on the Western Theater of the American Civil War.

Category:Units and formations of the Union Army