The mouth of Eckernförde is a pretty good place to observe the main transit belt between the North Sea and the Baltic.<p>This monitoring station disappeared toward the end, or shortly after, a major Russian naval exercise involving almost all of their northern fleet.<p>The US has moved an aircraft carrier, the Harry S Truman, near the coast of Norway, perhaps to observe Russian activity.<p>The Russians have two diesel-electric boats, both Kilo class, in the Baltic. Apparently, one of them has been out of commission for a while. The rumour is that they're significantly upgrading their Baltic submarine fleet.<p>While no passive sonar function has been disclosed for this station, it is fairly new, expensive and high-tech. It was deployed recently as an upgrade to the German data collection system in Kiel Bay.<p>Perhaps the Russians wished to transfer nuclear submarines to the Baltic to upgrade their fleet, and this station was seen as a concern.