The ruined base is a bearing on the map of the Swamp Sector. It marks the point of a base that had an large explosion, which destroyed it almost completely. Strong electromagnetic abnormality prevented the others to go there.
The anomaly got weaker, so the Swamp Sector's main base wants the player in its first mission to record the anomalies coming out from there. The bearing gets placed after accepting this mission.
The records say that the base was destroyed by a radiation of unknown source which was located in the underground of the sector.
Location of the ruined base on the map.
Sunken turret in swamp.