The executive officer (or XO) is a billet position in the armed forces. They are considered command positions, and is always the officer that is junior to the commanding officer.
In the UNSC Navy, the executive officer (or First officer) is the senior most crew member below the commanding officer of the ship. Usually, this post will be held by a Commander or Lieutenant Commander, but occasionally will be held by a Lieutenant.
UNSC Army and Marine Corps
In the UNSC Army and Marine Corps, the executive officer is the officer that is second-in-command to the commanding officer. Executive officer billets exist from the company level up, in both the Army and Marine Corps.
Note that platoons do not have XOs; the second-in-command in a platoon is a platoon sergeant.
Known executive officers
- First Lieutenant Melissa McKay, ODST division on the UNSC Pillar of Autumn
- Commander Richard Lash, UNSC Dusk
- Lieutenant Commander Julian Waters, UNSC Dusk (Acting)
- Lieutenant Commander Nevel, CMA Season of Plenty
- Commander Thomas Lasky, UNSC Infinity (Promoted to Captain of Infinity)
- Commander Bradley, UNSC Infinity
- Terrence Hood, UNSC Spirit of Fire (Transffered and Promoted as Captain on UNSC Roman Blue)
- First Lieutenant Maher, UNSC Dark Was the Night (acting)
- Halo: The Flood, Chapter 3, page 91 (2003 paperback); page 102 (2010 paperback)
- Halo: Ghosts of Onyx, page 185
- Halo: Ghosts of Onyx, page 187
- Halo: Evolutions - Essential Tales of the Halo Universe
- Halo: The Thursday War, page 48
- Halo: Escalation, Issue #2
- Halo: Escalation, Issue #5