Lieutenant Commander is a traditional naval rank. It was once used in the old navies of Earth, among them the United States Navy and the Royal Navy. In these organizations, a lieutenant commander was a grade between the ranks of lieutenant and commander.
By the 22nd century, lieutenant commander had apparently become defunct and was not used in the Earth Starfleet. A century later, in the early 2260s, lieutenant commander was being used by the Federation Starfleet.
A lieutenant commander can serve as either the commanding officer or executive officer of small- to medium-sized vessels or serve as the department head (in addition to being the second officer or third officer) onboard a larger vessel.
Rank insignia of Starfleet lieutenant commandersEdit