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.