XV Corps (Union)

XV Corps (Union)
Unit name	XV Corps
Dates	1862–1865
Country	United States
Allegiance	Union
Branch	United States Army
Type	Corps
Role	Field army corps
Notable commanders	William T. Sherman, John A. Logan, Peter J. Osterhaus

XV Corps (Union) was a corps of the Union Army during the American Civil War formed in late 1862 that served primarily in the Western Theater, participating in major campaigns including the Vicksburg campaign, the Chattanooga campaign, the Atlanta campaign, and the March to the Sea. The corps served under senior commanders such as Ulysses S. Grant, William T. Sherman, and George H. Thomas, integrating divisions and brigades from states across the Midwest United States, and contributing to strategic operations that culminated in the Appomattox Campaign and Confederate collapse.

Formation and Organization

The corps was created by order of Henry W. Halleck and the War Department during the reorganization of the Army of the Tennessee following the Battle of Shiloh and the Siege of Corinth, drawing regiments from Illinois, Iowa, Wisconsin, Missouri, and Ohio. Initially organized under the command structure of the Army of the Tennessee, the corps' headquarters coordinated infantry, artillery, and limited cavalry elements during operations led by commanders including John A. McClernand and Ulysses S. Grant. The organizational framework followed contemporary Union corps models established after the Second Battle of Bull Run, with divisions broken into brigades commanded by officers such as John A. Logan, Peter J. Osterhaus, and James B. McPherson.

Commanders and Leadership

Commanders who led the corps included John A. Logan (interim), William T. Sherman during portions of the Vicksburg campaign, and others including Peter J. Osterhaus, John A. Rawlins (staff oversight), and division leaders who rose to prominence such as Jacob G. Lauman and Morgan L. Smith. The corps' leadership worked within the command nexus of Ulysses S. Grant and later William T. Sherman, coordinating with corps commanders from the Army of the Cumberland like George H. Thomas and contemporaries in the Army of the Ohio such as Ambrose Burnside. Staff officers and brigade commanders were integral in translating orders from the Department of the Tennessee into tactical deployments during operations around Vicksburg, Chattanooga, and across Georgia.

Campaigns and Battles

The corps played a prominent role in the Vicksburg campaign, participating in assaults and siege operations that culminated in the surrender of Vicksburg, Mississippi and the strategic control of the Mississippi River. During the Chattanooga campaign, elements of the corps were engaged in maneuvers linked to the Battle of Missionary Ridge and operations that relieved the besieged forces at Chattanooga, Tennessee, coordinating with George H. Thomas and James B. McPherson. In the Atlanta campaign, the corps conducted flanking movements, fought in actions near Kennesaw Mountain, and contributed to the capture of Atlanta, Georgia, operating under the grand strategy of William T. Sherman. The corps then took part in the March to the Sea and the subsequent Carolinas campaign, contributing to the occupation of Savannah, Georgia and actions leading to the surrender of Confederate armies under Joseph E. Johnston and the eventual meeting with forces at Appomattox Court House under Ulysses S. Grant.

Order of Battle and Units

Throughout its service the corps comprised divisions and brigades formed from regiments such as the 20th Illinois Volunteer Infantry Regiment, 24th Iowa Volunteer Infantry Regiment, 37th Illinois Volunteer Infantry Regiment, and the 15th Wisconsin Volunteer Infantry Regiment, among many others drawn from Indiana, Michigan, and Missouri. Artillery batteries attached to the corps included units raised in Illinois and Ohio, while cavalry detachments from Missouri and Kentucky provided reconnaissance and screening. Commanders at division and brigade level—figures like John A. Logan, Peter J. Osterhaus, Samuel Ryan Curtis (as contemporary departmental commander), and Morgan L. Smith—oversaw tactical formations that adapted between siege operations at Vicksburg and mobile operations during Sherman's March.

Casualties and Strength

The corps' strength fluctuated through reenlistments, conscription policies enforced by the Enrollment Act and battlefield losses sustained at operations including Jackson, Mississippi, Missionary Ridge, the Atlanta campaign, and the Carolinas campaign. Casualty rolls recorded thousands killed, wounded, and missing across sieges and frontal assaults, with attrition compounded by disease common in Civil War campaigns such as dysentery and typhoid fever that affected units drawn from Midwestern states. Strength reports filed to headquarters in the Department of the Tennessee and consolidated in returns under Ulysses S. Grant show cyclical replenishment via state regimental recruitment and transfers from neighboring departments like the Department of the Cumberland.

Legacy and Historical Assessment

Historians assessing the corps emphasize its operational flexibility and contributions to strategic victories in the Western Theater that undermined Confederate control of the Mississippi River and facilitated the capture of Atlanta and the destruction of Southern infrastructure during the March to the Sea. Scholarly works connecting the corps' activities to Union strategic success include analyses of William T. Sherman's operational art, studies of the Vicksburg Campaign by Edwin C. Bearss and others, and broader syntheses of Civil War command by historians such as James M. McPherson and Eric Foner. The corps' veterans influenced postwar memory through participation in Grand Army of the Republic posts and veterans' reunions, contributing to commemorations at sites like Vicksburg National Military Park and Chickamauga and Chattanooga National Military Park.

Category:Corps of the Union Army