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Commander is the second highest line officer rank. Ranking above Lieutenant Commander and below Captain. It has a ranking code of O-5 and is equivalent to Lieutenant Colonel in the Starfleet Marine Corps. The rank insignia consists of three full pips. Officers holding the rank of Commander are generally highly respected by their peers.
Commanders are most regularly seen as Executive Officers on starships or starbases, or as a senior Department Head. Often though, Commanders can be found as junior commanding officers in the fleet, found on various starships and, occasionally, in command of small starbases. Commanders who aren't assigned to an active duty post are often found as senior assistants in Starfleet departments on major worlds.
In Starfleet, a prerequisite to becoming a commander is by taking the Bridge Officer's Test. As commanders prove their leadership ability over time, they are considered for the difficult and highly competitive promotion to captain.