As a Union Army artillery officer in the American Civil War, his performance was notable at the Battle of Stones River, where his concentration of guns broke the last Confederate attack.

At the outbreak of the war, MG John E. Wool retained Mendenhall to train artillery recruits.

Mendenhall first saw combat commanding batteries H and M of the 4th Artillery in the Army of the Ohio, supporting the division of Brig.

[2] Several senior officer, including MG Don Carlos Buell, the army's commander, praised Mendenhall and his gunners for outstanding work.

The 45 guns plus another dozen in enfilading position broke the Confederate attack and relieved the threat to the federal left.

[8] After the war, Mendenhall served in Michigan, the Carolinas, California, Alaska, Massachusetts, Rhode Island, New York, and Connecticut.

He left his widow and three grown sons: Clarence Miles, Theodore John, and Leo Thomas Crittenden.