Laboratory analysis fails to reveal source of unusual underwater sound.

The Finnish Navy searched for a possible submarine in the coastal waters just south of the capital Helsinki a little over a week ago.

The search began after an unusual sound was detected by the Naval Underwater Surveillance Unit on the island of Isosaari, just ten kilometres off central Helsinki, at nine o'clock in the evening of Saturday, August 5th. The search for the elusive audio trace continued well into the following day.

A Rauma-class missile boat and the Coast Guard vessel Merikarhu were dispatched to look into the source of a sound signature atypical to surface vessels.

Neither of the ships found anything unusual.

A naval laboratory later analysed the recorded sound, but failed to establish its source.

The possibility of a submarine cannot be eliminated, but the explanation for the sound signature can also be biological, Commodore Tapio Maijala believes.

According to Maijala, this was the largest search of its kind this year.

At the time of the incident, the underwater audibility was exceptionally good because of the prolonged hot and calm weather. In such conditions sound perceptions can be detected from tens of kilometres away.

According to Lieutenant-Commander Jukka Alavillamo, a few submarine detections are made each year in the Gulf of Finland naval defence area. Alavillamo refrained from commenting on how many of these detections are in Finland's territorial waters.

Unlike violations of Finnish airspace, submarine searches are not actively announced, as getting conclusive proof of underwater violations of territorial waters is extremely difficult.

"We can only talk about definite observations if the submarine surfaces, or if we get an image using active sonar", Alavillamo explains.

Numerous submarine sightings were made in Swedish coastal waters in the 1980s, but the only definite finding was the Soviet submarine that ran aground near Karlskrona in 1981.

Of the Baltic Sea countries, only Russia, Sweden, Poland, and Germany have submarines.

Russian submarines from the naval base in front of St. Petersburg are seen from time to time on the surface on their way to training exercises.

According to newspapers, Russia tested a new, fourth-generation submarine from the St. Petersburg base last winter. The new vessels, the production of which is running years behind schedule, are meant to replace the antiquated models currently used by the Russian Navy. Export models are also aimed for the international market.

Public domain sources reveal that the Russian Baltic Sea Fleet has presently three to four operational submarines.

News source: hs.fi
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