In Starfleet, the navigator holds the position responsible for projecting the course of a starship, and for determining a ship's position, velocity and direction in relationship to a course. The navigator can also use the ship's navigational sensors to determine the positions, speeds and trajectories of other objects. Additionally, in the 2250s and 2260s, a navigator was in charge of coordinating phaser crews for real and simulated combat and for firing the weapons. (TOS: \"The Corbomite Maneuver\", \"Obsession\") By the end of 2266, this last function had shifted to the helmsman. (TOS: \"Balance of Terror\")
On Earth Starfleet's NX class starships, navigation was handled by the helmsman. (Star Trek: Enterprise)
On Federation Starfleet vessels of the 23rd century, the navigator was a bridge officer, while the helm officer's role was usually combined with that of the tactical officer. (Star Trek: The Original Series)
By the 24th century, navigator responsibilities were once again merged with those of the helmsman to form the position of flight controller, or conn. (Star Trek: The Next Generation). It should also be noted that Data also held Navigational duties and the occasional helmsman duties aboard the USS Enterprise-D, in addition to his role as operations manager; though usually only in an emergency situation.