Subcommander is a military rank most commonly used in the Star Trek mythos. It is used by certain alien organizations such as the Romulan Star Empire and their distant cousins, the Vulcan High Command. The Romulan rank of subcommander is fully equal to a Federation Starfleet captain. In joint operations with Earth Starfleet, a Vulcan subcommander has been treated as being a grade below a Starfleet captain and above a Starfleet commander. The rank was first identified in the season one episode of the original Star Trek series, "Balance of Terror". The rank was also used in the "Space Fall" episode of Blake's 7.