Starfleet records. Starfleet ranks. First officer: Noted functions of the first officer aboard a Federation starship are (3): Take command of the starship in the event of the captain's absence, incapacitation or death. Sources: TOS: "The Squire of Gothos", "Journey to Babel"; VOY: "Before and After", "Scorpion, Part II", "Night", "Tsunkatse", "Unimatrix Zero", "Unimatrix Zero, Part II"; TNG: "The Battle", "The Best of Both Worlds", "The Best of Both Worlds, Part II", "Tapestry", "Gambit, Part I"

Starfleet records. Starfleet ranks. First officer: Coordinate personnel transfers between departments. Source: TNG: "Lessons". Star Trek. Live the experience. Star Trek: PICARD - Season 4 #StarTrekLegacy | Starfleet Command

Starfleet records. Starfleet ranks. Second officer: Still later that year, Bjorn Bensen, the chief engineer of Velara Base, was intrigued by Data, asking if he was an android. Tasha Yar, answered that he was, and added that additional he was "third-in-command of the Enterprise." Source: TNG: "Home Soil". On several occasions thereafter, he is introduced as the ship's second officer. Sources: TNG: "First Contact", "Time's Arrow", "Starship Mine". Star Trek. Live the experience. Star Trek: PICARD