Sierra VI
Sierra 6, also known as Outpost Sierra 6, was a Federation outpost administered by Starfleet that was near the Romulan Neutral Zone.

In 2366, the Federation starship  detected a Romulan scout ship in the Romulan Neutral Zone. This outpost confirmed the presence of the scout ship and sent a message to the Enterprise-D. After receiving intelligence from a Romulan defector about a possible Romulan base at Nelvana III, this outpost received a warning from Starfleet Command. ()

See also 
 Starbase 39-Sierra

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Romulan Neutral Zone
Outposts