Commanding officer

The Commanding Officer is a billet position filled by officers that are in command of a particular duty, such as commanding a UNSC starship or leading a Marine unit. The status of commanding officer is duly applied to all commissioned officers who hold lawful command over a military unit, ship, or installation. Before a Naval officer is given control of a starship, they usually are given the rank of Captain.

In the Navy, commanding officer is the official title of the commander of a ship, but they are usually referred to as "the Captain" regardless of their actual rank, or informally referred to as "skipper". However, there have been Navy COs that held the rank of Commander, such as Captain Keyes before his promotion to Captain during the Battle of Sigma Octanus IV. Marine Commanding Officers are issued orders by a higher ranking Naval Commanding Officer if on-board a starship. Marine Battalion COs (known as Battalion commanders) are usually Lieutenant Colonels, though Majors can fill this position if a Lieutenant Colonel is unavailable. Marine Platoon commanders are usually First Lieutenants, and company commanders are usually Captains.

Commanding officers may be of any commissioned rank. Usually there are more officers than command positions available, and time spent in command is generally a key aspect of promotion, so the role of commanding officer is highly valued, and in theory only goes to the best officers. In a unit, the commanding officer is often assisted by an executive officer (XO) or Second-in-Command (2i/c), who handles personnel and day-to-day matters. Larger units may also have staff officers of various responsibilities. Commanding officers are one of many billet positions that are allowed into officer's quarters.

In the UNSC Army, the commanding officer of a platoon is referred to as a Platoon Leader. The commanding officer of a company is referred to as a Company Commander, the commanding officer of a battalion is referred to as a Battalion Commander, and the commanding officer of a brigade is referred to as a Brigade Commander. At the division level and higher, however, the commanding officer is referred to as the Commanding General, as these officers are normally general-grade officers.

Known Naval Commanding Officers
NOTE: The list is incomplete.

Fleet Admiral
 * Terrence Hood (Fleet Admiral, CO of the UNSC Home Fleet)
 * Harper
 * H.T. Ward

Admiral
 * Carl Patterson
 * Dale Kilkin
 * Harold Stanforth
 * Konrad Volkov
 * Preston Jeremiah Cole
 * Roland Freemont
 * Ysionris Jeromi

Vice Admiral
 * Alexander Reaves
 * Berlin M. Tursk
 * Danforth Whitcomb
 * Gerov
 * Jean Mawikizi
 * Kopano N'Singile
 * Margaret Orlenda Parangosky
 * Michael Stanforth

Rear Admiral
 * Ned Rich
 * Saeed Shafiq

Captain
 * Aaron G. Gibson
 * Damien Hogarth
 * De Blanc
 * D. F. Lambert
 * Edgar Sykes
 * Greene
 * Iglesias
 * Jacob Keyes
 * James Gregory Cutter
 * Jenkins
 * Kristòf Jen
 * Lucius R. Jiron
 * Maria F. Gilliam
 * Maribeau Veredi
 * Moreland
 * Serin Osman
 * Veronica Dare
 * Wallace

Commander
 * Arthur Resnick
 * Carter-A259
 * Dmitri Zheng
 * Hadley
 * Jerome G. Ortega
 * Pasquale
 * Richard Lash
 * Rinkishale
 * Theo Figueroa
 * Tobias Foucault
 * Unidentified Commander (Living Monument)

Lieutenant Commander
 * Catherine-B320
 * Fhajad-084
 * Gail Purdy
 * Jack Hopper
 * Julian Waters
 * Jilan al-Cygni
 * Kurt-051
 * Miranda Keyes
 * Xaing Cho

Lieutenant
 * Akita Hikowa
 * Badia Campbell
 * Bethany Durruno
 * Dante Kirtley
 * Demos
 * Elias Haverson
 * Green
 * Jaggers
 * Joe Yang
 * Jorgenson
 * Maliki
 * Rick Hale
 * SPARTAN-B312
 * Wagner
 * W. K. Davidson

Lieutenant Junior Grade
 * Bill Streeter
 * David Brightling
 * Fredric-104
 * Rai Li

Known Marine/Army commanding officers
NOTE: This list is incomplete.
 * Kits (Marine/General)
 * Nicolas Strauss (Marine/Major General)
 * James Ackerson (Army/Colonel)
 * Unnamed UNSC Colonel (Marine/Colonel)
 * Antonio Silva (Marine/Major)
 * Melissa McKay (Marine/First Lieutenant)
 * Avery Junior Johnson (Marine/Sergeant Major)
 * Edward Buck (Marine/Gunnery Sergeant)
 * Urban Holland (Army/Colonel)
 * Jake Chapman (Marine/First Lieutenant)
 * Stacker (Marine/Gunnery Sergeant)
 * John Forge (Marine/Sergeant)
 * Ponder (Marine/Captain)
 * Felicia Sanderson (Marine/Colonel)
 * Aboim (Marine/Lieutenant Colonel)
 * Nolan Byrne (Marine/Staff Sergeant)
 * Duvall (Army/Sergeant Major)
 * Akio Watanabe (Marine/Major)
 * Canfield (Marine/First Lieutenant)
 * Harland (Marine/Corporal)
 * Marvin Mobuto (Marine/Staff Sergeant)
 * Thomas Chang (Marine/Sergeant)
 * Roland Huffman (Marine/Major)
 * Lian Devereaux (Marine/Sergeant)
 * Malcolm Geffen (Marine/Staff Sergeant)
 * K. Stark (Marine/Staff Sergeant)
 * Reynolds (Marine/Gunnery Sergeant)
 * Unidentified Master Gunnery Sergeant (Marine/Master Gunnery Sergeant)
 * Akono Menteith (Army/Colonel)
 * Waller (Marine/Gunnery Sergeant)
 * Cortez (Marine/Master Sergeant)
 * Frost (Marine/Master Sergeant)
 * Teller (Marine/Colonel)