Commanding officer

Commanding Officers are a role filled by officers that are in command of a particular duty, such as commanding a UNSC starship or leading a Marine division. 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 before such control is given. 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 known 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 COs are issued orders by the usually higher ranking Naval COs if on-board a starship. Marine Battalion COs are usually Majors or Captains. Marine Platoon COs are usually Lieutenants.

Known Navy Commanding Officers
NOTE: The list is incomplete.
 * Jacob Keyes (Captain)
 * Danforth Whitcomb (Vice Admiral)
 * Miranda Keyes (Commander)
 * Fleet Admiral Harper
 * Jilan al-Cygni (Lieutenant Commander)
 * Lord Hood (Fleet Admiral, CO of the UNSC Home Fleet}
 * SPARTAN-051 (Lieutenant Commander)

Known Marine/Army Commanding Officers

 * Antonio Silva (Major)
 * Melissa McKay (Lieutenant)
 * James Ackerson (Colonel)
 * Nicolas Strauss (Major General)