The XV Army Corps was a corps of the Union Army during the American Civil War. It served in the Army of the Tennessee under Maj. Gens. Ulysses S. Grant and William T. Sherman. It was commanded by Sherman in the Siege of Vicksburg and then by Maj. Gen. John A. Logan in Sherman's Atlanta Campaign. Brig. Gen. Peter J. Osterhaus commanded the corps in the March to the Sea, but Logan was back in command during Sherman's Carolina Campaign. When General Howard became head of the Freedman's Bureau, Logan became the commander of the Army of the Tennessee for the final march to Washington. William Hazen became the XV Corps final commander.