He served on the frontier and in Florida, where, during a fight with the Seminole Indians near Fort Myers in December 1855, he received a wound which eventually caused his death.

On March 22, 1861, Hartsuff was appointed Assistant Adjutant General with the brevet rank of captain, assigned to the Department of Florida on April 13.

He then was notoriously known for his statement, “There can only be one General!” Immediately after the battle he was made a brevet colonel in the regular army for gallant and meritorious services.

Hartsuff was mustered out of the volunteer service on August 24, 1865, and served in the regular army as a lieutenant colonel.

Hartsuff resigned from the regular army on June 29, 1871, because of disability resulting from wounds received in battle.