Sub-commander
Sub-commander was a military rank used by the Vulcan High Command and the Romulan Star Empire.

Among Vulcan ranks, sub-commander fell between major and captain. In joint operations with Earth Starfleet, sub-commander was treated as being a grade between a Starfleet captain and commander. () The conversion of the rank, when an officer was integrated into Starfleet, was brought down slightly, to the rank of commander. (, et al.)

Following Sub-Commander T'Pol's resignation from the Vulcan High Command and joining Starfleet as a commander, she was captured by Administrator V'Las's forces while hiding in Vulcan's Forge in 2154. Upon her surrender to the High Command, V'Las addressed her by her former rank of "sub-commander", but she rebuked his statement, replying that "I no longer hold that rank." He dismissed her correction and explained, "Well, you may have joined Starfleet, but you're still Vulcan. And subject to our laws." ()

Among Romulan ranks, sub-commanders were ranked below commanders and above centurion, and could hold the position of either first officer or commanding officer. (; ; )

Sub-commanders 
 Romulan Star Empire
 Almak
 N'Vek
 Selok
 
 Taris
 Thei
 T'Rul
 Ustard
 Velal
 Vulcan High Command
 Muroc
 T'Pol

Appendices

Background information 
The name used first, and most often, in Star Trek scripts was "Sub-Commander", but it is also common to see it spelled as "Subcommander". Monitor displays, such as in , used the spelling "Sub-commander".

According to The Making of Star Trek (p. 256), the Romulan rank of sub-commander is fully equal to a Federation Starfleet captain.

In the first draft script of , Donatra was another Romulan subcommander, though her rank was ultimately changed to that of commander.

References 
 (ENT Season 1)

 (ENT Season 2)

 (ENT Season 3)

 (ENT Season 4)

 (TOS Season 3)

 (TNG Season 2)
 (TNG Season 4)
 (TNG Season 6)

 (DS9 Season 3)

 (DS9 Season 4)
 (DS9 Season 7)

 (VOY Season 4)

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Military ranks