Chief tactical officer was a senior position for Starfleet officers on board starships and starbases. Tactical officers were in charge of tactical operations, including weapons and shields, and ship's security.
On board Constitution-class starships in the early to mid 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). However, from the 2270s the tactical station was added to the bridge, from which was controlled the photon torpedoes and deflector screens. (Star Trek: The Motion Picture; Star Trek II: The Wrath of Khan)