Second officer
The second officer was an officer who was third in command of a starship and who assumed command of the ship when both the captain and first officer were unavailable.

It was standard procedure for a Starfleet second officer to accompany the away team. ()

Ferengi code was to offer the life of their second officers when surrendering. When Lieutenant Commander Data, second officer of the , learned of this code in 2364, he stated to Geordi La Forge, "Fortunately, Starfleet has no such rules involving our second officers." () 

During a second encounter with the Ferengi that year, Data was introduced to Bok by Captain Jean-Luc Picard as his "second-in-command", after Bok's own second officer was Rata was introduced. () 

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." () 

On several occasions thereafter, he was introduced as the ship's second officer. ()

On Klingon warships, the first officer was called upon to ensure their incapacitated captain died an honorable death. In 2365, Worf explained to William T. Riker that should he also become unable to perform while serving as an exchange officer, his second officer would kill him. ()

When the Satarran agent using the alias of Kieran MacDuff commandeered the Enterprise in 2368, he altered the computer records so that the ship's rightful first officer, Commander Riker, was listed as the second officer. ()

List of second officers
 Lieutenant Commander Data ()
 Lieutenant Commander Jadzia Dax (; implied)
 Lieutenant  ()
 Rata (Bok's Marauder)
 Lieutenant Commander Saru (; implied)
 Lieutenant Commander Montgomery Scott (; implied)
 Spock (USS Enterprise, 2254; implied)
 Timothy's father ()
 Commander Charles Tucker III (; implied)
 Lieutenant Commander Tuvok (; implied)
 Lieutenant Commander Worf (Deep Space 9; implied)
 Major  (; implied)

See also  
 Second officer's log
 Second officer's personal log
 Second officer's science log

External link
 

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es:Segundo Oficial
ja:第二副長
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ru:Второй помощник
Titles
Military ranks