Second Officer

Whether aboard a starship or a space station, a second officer assumed command when both the captain and first officer were unavailable.

It was common for a second officer on a Star Fleet vessel or other installation to hold the rank of lieutenant commander. The second officer was a department head first, and a second officer second. They are rarely involved in the day-to-day command of the starship or starbase the way the captain or first officer was. It was standard procedure for the second officer to accompany away teams.