The XIV Corps was to be organized from troops of the Army of the Cumberland, and to be commanded by General William Rosecrans.

The III Corps became the Center Wing under George H. Thomas, replacing Charles C. Gilbert.

In this formation the corps fought at the Battle of Stones River losing over 25% in killed, wounded or missing.

Thomas led the corps to distinction for his defense at Horseshoe Ridge (in particular his actions at Snodgrass Hill) protecting the Federal Army from a complete rout following the Battle of Chickamauga.

Following Chickamauga, Thomas was given command of the Army of the Cumberland and John M. Palmer led the corps at the Battle of Missionary Ridge and during most of the Atlanta Campaign.