Second officer

The Second Officer, or 2O is operationally the ship's third-in-command of a Starfleet unit, be it a starship or a space station, and will immediately assume command if anything renders the Commanding Officer and Executive Officer unfit for duty. A Second Officer's chief duty is to carry out the CO's and XO’s orders. The 2O is often the closest officer to the XO and the CO due to the three generally being the most senior officers aboard. As such, the 2O also often acts as the CO's second conscience and confidante. It is another primary duty of the Second Officer to spearhead secondary away teams, with the XO leading the primary away team, should situations merit two away teams at one time. This is so that the CO can remain safe in the confines of the bridge. The 2O is the assistant chief administrative officer on the ship and frequently helps the XO act as liaison between department heads.

Unlike the CO and XO, Second Officers are usually department heads and hold the rank of Lieutenant, Lieutenant Commander or even Commander. But for the very large capital ships belonging to the Heavy Battleship, Fleet Carrier, and Fleet Carrier-Battleship Hybrids, Second Officers act more as alter egos of the XO, do not occupy department head positions, and hold the rank of Commander or Captain.

Considering that the new capital ship classes have very large crew complements, one of the Second Officer's chief responsibilities is to help the XO in the performance of his/jer duties in the training, discipline and management of the ship's personnel. In that capacity, the 2O makes his/her own recommendations for promotions and transfers based on inputs from the crewmember's department head.