Earth Outpost 4 was one of several United Federation of Planets facilities monitoring the Romulan Neutral Zone. Four facilities -- Earth Outposts 2, 3, 4 and 8 -- were destroyed on stardate 1709.2 by a single Romulan Bird-of-Prey testing the Federation's military strength with a plasma weapon. (TOS: "Balance of Terror") This outpost was commanded by Commander Hansen until the incursion of 2266. Earth Outpost 4 was apparently replaced. 20 years later, USS Konkordium was called to act as backup to USS Avenger during a standoff at Earth Outpost 4. (Star Trek: Avenger: "By Honor Bound")