After his brother's departure, Bender enlisted in the United States Army at the age of eighteen on June 10, 1854, changing his name to Charles Bendire, dropping his middle name altogether. Although Bendire would later start using his middle initial again in correspondence and public notes, his legally official name did not contain a middle name. Bendire served for five years as a private and subsequently a corporal in Company D, First Dragoons. After his tour of duty ended Bendire left the army for one year, but re-enlisted on June 8, 1860, and was assigned to the 4th Cavalry, where he served successively as a private, corporal, sergeant, and a hospital steward until he was commissioned as a 2nd Lieutenant in the 2nd Infantry on May 18, 1864. He transferred to the
1st Cavalry on September 9, 1864, and was eventually promoted to 1st Lieutenant (for "gallant and meritorious services" at the
battle of Trevilian Station during the
American Civil War), and later to captain, and then major. He retired on April 24, 1886, for disability contracted in the line of duty. During Bendire's service in the army he was sent to many locations, often isolated, across America, for example
Virginia,
Arizona,
Oregon,
Washington, and
California. Bendire mainly fought against
American Indians during the periods of the United States' expansions. It was during these travels across North America that he developed a fondness for all things wild, and particularly
birds. ==Ornithology==