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Lieutenant Commander is the first line officer rank deemed to be a 'senior officer', ranking above Lieutenant and below a full Commander. It has a ranking code of O-4 and is equivalent to a Major in the Starfleet Marine Corps. The rank insignia consists of two full pips and one hollow pip. Officers holding the rank of Lieutenant Commander generally hold high respect amongst their peers.
Lieutenant Commanders are most regularly seen as Executive Officers on starships or starbases, or as a senior Department Head. Often though, Lieutenant Commanders can be found as junior commanding officers of very small craft within the fleet. A Lt. Commander may command a larger vessel or even a starbase whilst attending the Command Course of Starfleet Academy. Lt. Commanders who aren't assigned to an active duty post are often found as senior assistants in Starfleet departments on major worlds.