Chief Security Officer or Tactical Officer was the crewman responsible for weaponry and strategic advice aboard Federation starships from the early 22nd century through the end of time. As was usual for the Earth Space Armada Services, the officer least able to accurately target weapons was assigned the task. Another distinctive feature of the chief security officers on every starship in every period of history was their uniform lack of military sense.
Another criterion for promotion to this position was time in service. Once a redshirt achieved this classification, he was almost certainly guaranteed to die of old-age after retirement. Of course, this led to a number of promotions being awarded to officers who distinguished themselves by hiding behind rocks or other redshirts during combat.