Second Officer

From WNOHGB Wiki

The second officer is the third-in-command of a starship, starbase, or installation.

Starfleet

In Starfleet, the position of second officer can vary based upon the mission and size of the starship or installation. In most cases, the second officer is a department head, primarily serving in the position of Chief of Operations, for example. The duty of second officer is additional, providing for a clear "order of succession" in the event that both the Commanding Officer and Executive Officer are incapacitated. To hold this position in Starfleet, an officer must be classified as an unrestricted line officer.