Epsilon Monitoring Station

The Epsilon Monitoring Stations were a series of observation and communications relay stations built along the Federation/Klingon border. At least nine of these were in service by the 2278s. 

In April, 2288, Epsilon 3 advised USS Avenger of a group of Klingon vessels paralleling Avenger 's patrol group, but on the Klingon side of the border. (: "Border Skirmish")

Epsilon 9, and its officers and crew, was destroyed by V'Ger while the latter was en route to Earth.