Executive Officer

Aboard a starship the first officer was the second-in-command, just below the captain. On a Starfleet starship, the first officer had the following functions:

• the principal adviser to the captain
• implementer of the captain's orders
• preparation and issue of duty rosters
• commander of the vessel in the event of the captain's absence, incapacitation or death
• work with the chief medical officer on crew evaluations

In Starfleet the position was usually held by an officer with the rank of commander or lieutenant commander. The position was also referred to as executive officer, or XO

In Starfleet's early period of existence, the first officer would accompany the captain on landing parties, depending on the situation.