 Complete the following phrase:  Garfield later served under Major General Don Carlos Buell at the Battle of Shiloh and under Thomas J. Wood at the siege of Corinth. Garfields health deteriorated and he was sent to serve on a commission to investigate the conduct of Union general Fitz John Porter. In the spring of 1863, Garfield returned to the field as chief of staff for William S. Rosecrans, commander of the Army of the Cumberland. After the disastrous 