Commander is a military rank or title, and was used in several different ways during the era of the Clone Wars, Galactic Civil War and Yuuzhan Vong invasion, as well as other wars.
Military usage[]
As a generic mode of address, "commander" was appropriate to many military officers - almost anyone holding a distinct unit or ship command could be called "commander" in this way, although the commanding officers of capital ships usually preferred to be addressed as "Captain". Alongside this generic usage, "Commander" was also used as a specific rank, with several different meanings depending on the context.
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In many naval hierarchies, including those of the Old Republic, the Galactic Empire, the Rebel Alliance, the New Republic and the Galactic Alliance, a Commander ranked above a Captain.