In the first Mass Effect game, After obtaining the Normady when you leave the Ship's VI says

XO Presley has the Deck.

and when you return it says

XO Presley stands relived.

Now i am assuming that since Shepard is the commanding officer Presley is second-in-command who takes command when Shepard is off the ship so when he returns Presley is relived of his command.

From my understanding, it's common that space-operating organizations in Sci-Fi are associated with the Navy (Time Space Administration Bureau's Dimensional Navy in Magical Girl Lyrical Nanoha, UNSC Marines in Halo and generally outer-space combat fights refereed to as Marines where Marines are normally under the jurisdiction of the Navy) but i don't think i've heard the term XO refereed to a second-in-command rather normally their rank is used

So what does XO mean? (like how CO = Commanding Officer)

  • 1
    Google for "XO military" or "XO navy" - Null's link is the very first result
    – Izkata
    Sep 11, 2014 at 1:20
  • 8
    This question appears to be off-topic because it is about military terminology, not something specific to sci-fi
    – HorusKol
    Sep 11, 2014 at 2:30
  • 1
    @HorusKol the question was mainly about the use of XO in Mass Effect, i added the part about the Navy as from my observations Sci-Fi tends to use the Navy as a base command structure for space-operating organizations and thought that XO may not be entirely just Sci-Fi/Mass Effect lingo
    – Memor-X
    Sep 11, 2014 at 2:36
  • 3
    There are many other examples of its use across sci-fi and non-sci-fi works in many different formats (TV, film, book, games) - so I still feel the question is not on-topic here, sorry.
    – HorusKol
    Sep 11, 2014 at 2:41

1 Answer 1


XO is a common abbreviation for Executive Officer.

  • Ahhh, the X is being used in it, when i initially saw Executive Officer i thought it similar to a Chief Executive Officer which is CEO and thought it incorrect to what i was looking for
    – Memor-X
    Sep 11, 2014 at 1:27

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