From Halopedia, the Halo wiki
Captain, abbreviated to CAPT, is a commissioned officer rank of O-6 in the United Nations Space Command Naval Command (NAVCOM) rank structure; including the UNSC Navy and Office of Naval Intelligence. It is preceded by Commander, and subordinate to a Rear Admiral.[1]
Captain of line warship or installation.[1] Captains have also been shown to command entire fleets and battle groups, an example being Captains Andrew Del Rio and Thomas Lasky commanding the Expeditionary Strike Group 1 Fleet and Captain Maribeau Veredi commanding Battle Group 4.
Captain - Halo CE (Keyes's medal ribbons).
Captain - Halo 4 (Angle 1)
Captain - Halo 4 (Arm stripes)
Captain - Halo 5: Guardians (Pre-rendered)
Captain - Halo 5: Guardians (Angle 1)
Captain - Halo CE (Keyes)
Captain - Halo Wars 2 (Cutter)
Captain - Halo 4 (Del Rio)
Captain - Halo 5 (Lasky)