A long-serving Federation starbase on a planet in the Gamma 400 system, referred to from the original series through to Picard as a command base near the Romulan border.
Starbase 12 is a Starfleet installation on a planet in the Gamma 400 system. It is one of the most often mentioned starbases, although it is never properly seen.
In the original series episode Space Seed, Kirk sets course for it with the sleeper ship Botany Bay in tow, and in Who Mourns for Adonais? Uhura tries to report to it when the Enterprise is seized at Pollux IV. Discovery establishes that the Klingons attacked and occupied the base during the war of 2256 to 2257.
In The Next Generation, its unexplained two-day evacuation in 2364 is cited in Conspiracy as evidence of something wrong in Starfleet. The Enterprise-D is refitted there in Captain's Holiday, and Power Play records that an Admiral Narsu commanded it in 2167.