Chief tactical officer
From Memory Alpha, the free Star Trek reference
Chief tactical officer is a senior position for Starfleet officers on board starships and starbases. Tactical officers are in charge of tactical operations, including weapons and shields, and ship's security.
This position is an evolution of the armory officer position assigned to Earth Starfleet ships in the 22nd century. (Star Trek: Enterprise)
On board Constitution-class starships in the 23rd century, the tactical officer did not have a bridge station, as weapons control was handled by the navigator or helmsman when needed, and security was handled by the ship's security officers. (Star Trek: The Original Series, Star Trek: The Animated Series)
By the 24th century, tactical officers aboard Galaxy-class starships were also usually charged with communications duties. (Star Trek: The Next Generation)
