Submarine sound - 12 October 1982


8 April 2010

Tape-recordings from the Sonar System at Mälsten, Stockholm Achipelago, 12 October 1982.

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Tape-recording from the Sonar System at Mälsten, Stockholm Archipelago, 12 October 1982. The tape recordings from the Swedish submarine incident on 11-14 October 1982 were made on five tapes (‘0’, ‘1’, ‘2’, ‘3’ and ‘4’). The recordings were made on the island of Mälsten at the exit from the Muskö naval base in the Stockholm southern archipelago. They used five hydrophones with a distance of 100-150 meters between each of them. We have only presented the recordings from hydrophone no. 3 (sound channel 3 on the tape), because of the amount of information that has to be downloaded. The attached files are from ‘Tape 1’. It starts at 9:13 in the morning on 12 October and ends at 18:16 the same day. The tape-recorder has been stopped and started again many times during this period. The first file (‘Tape 1a’) is about 20 minutes long. It starts at 9:13. In the beginning of the tape, after a few stops and starts, the speaker voice states that ‘it's 9:45’. There are no more statements on the spea-ker channel on this part of the recording. A helicopter passes the hydrophones after 14-15 minutes. After more stops and starts, at around the 18 minute mark, a small propeller starts twice, each time for 6-8 seconds. It is possibly a thruster on a submersible or small submarine. The position of this small propeller is estimated to be around 500 meter north of hydrophone no. 4 in the middle of Danziger Gatt. After that, there is a 1.5 minute recording of a propeller. This sound might originate from the same vessel. In that case, however, the sound would be from a regular propeller (not a thruster). ‘Tape 1b’ is a 3:47-minute long recording that might have been made as early as 10:30 but more likely at lunchtime or after lunch up to 16:30. The recording is characterized by a monotone propeller sound (the sonar operator has increased the volume for 45 seconds in the middle of the recording). The sonar operator does not make any comment on this recording. As opposed to the later recording, he does not say that he might be recording a submarine. However, for some reason, this sequence was later presented as a recording of a ‘Soviet submarine’. Early in the1990s, Swedish authorities presented it in Moscow as evidence of a ‘Soviet submarine’. Soviet authorities said that the propeller had three blades. It might not be a submarine, they argued, and it could under no circumstances have been a Soviet submarine. All Soviet submarines had at least five blades. In 2008, Swedish defence authorities made a new analysis of the tape and came to the conclusion that it probably originated from a small surface ship, the Amalia, with a three-bladed propeller. ‘Tape 1c’ is about 35 minutes long. It starts with an almost ten minute long recording of a twittering sound that, according to the documents, is supposed to start at 16:30. After that a comment follows on the speaker channel saying that ‘it is 17:50 …probable submarine’. After that, follows a 26 minute long recording with a lot of noise, thuds, metallic sounds and sounds from rudders and hydraulic valves. At 18:00, the sonar operator says to the staff at Mälsten that he is recording a ‘certain submarine’. Analysis made by specialists in recent years also shows that this is a ‘certain submarine’ recorded very close to the hydrophones. At 18:07 (after 26 minutes and 33 seconds on ‘Tape 1c’) one can hear a hydraulic valve closing, a distinct double metallic sound, that makes it possible to define the exact position of the valve and the submarine to be in between hydrophone no. 1 and 2, about 80 meters from hydrophone no. 2 (the sound appears first in no. 2, then 6 milliseconds later in no. 1, 67 milliseconds later in no. 3, and 150 milliseconds later in no. 4). When you know the position of the hydrophones you can also calculate the position of the sound. One minute later, it is about 40 meters from hydrophone no. 2. However, we have not identified any propeller sounds. The submarine is most likely gliding slowly, close to the hydrophones. There is a lot of noise from the submarine, particularly from 18:00 to 18:16. After that the sonar operator changes the tape. The speaker channel on tape 2 starts with: ‘continued recording of submarine. Four minutes for changing the tape’.