Outpost 2

From Memory Alpha, the free Star Trek reference.

Outpost 2 was one of a series of Earth Outpost Stations located in Sector Z-6 along the Federation side of the Romulan Neutral Zone.

In 2267, the Federation lost contact with the base. It was determined, by the USS Enterprise, that the station was destroyed by an unknown vessel that was later discovered to be a Romulan Bird-of-Prey. (TOS: "Balance of Terror")