Starbase 39-Sierra

Starbase 39-Sierra was a Federation starbase located near the Romulan Neutral Zone. 

While traveling to the Neutral Zone to investigate the disappearance of several outposts, Lieutenant Geordi La Forge suggested that a large portion of the USS Enterprise (NCC-1701-D)'s crew be left at this starbase in case there was a hostile encounter with the Romulan military.