Armory officers are those Starfleet personnel that command the weapons storage and operations facilities aboard a Federation starship, starbase or outpost. This job is part of the oversight of the operations division.
In the early days of Starfleet, there were no formal security commands set up on exploration vessels (such as the NX-class Enterprise NX-01), so the armory officer was often in charge of both tactical station functions and those of shipboard security. Many early policies of Starfleet security and tactical weaponry procedures were set in these early missions (such as the establishment of automatic tactical alert protocols coordinated by the ship's computer, devised by Armory Officer Malcolm Reed of Enterprise). The terms "armory officer" and "tactical officer" were used interchangeably, as the two jobs were occupied by the same person. (ENT: "Singularity")
The involvement of armory personnel in security operations lessened as MACO troops were assigned to Starfleet vessels during and after the Xindi conflict of the 2150s. Some functions of this department would, in later years, evolve into the modern Starfleet Security department, where many of the same roles played in the Earth Starfleet would be assigned to the position of security chief – which is sometimes occupied by the same individual who is chief tactical officer.
Technological aptitude is within the purview of the armory officer's skill base, including perfecting a force field's particle density, building phase cannons from scratch, possessing knowledge of demolitions, and repairing relays with a hyperspanner. (ENT: "Vox Sola", "Silent Enemy", "Minefield", "Proving Ground") By the 24th century, one security chief/chief tactical officer had such skill to develop unimatrix shielding. (VOY: "Extreme Risk")