Flights

Sea surveillance takes place, among other things, with NATO countries' submarine-hunting aircraft Poseidon P-8.

NATO surveillance aircraft AWACS also regularly fly in the Baltic Sea area.

Fixed surveillance

However, the fixed underwater surveillance systems are surrounded by high secrecy.

During the Cold War, lines with underwater microphones (SOSUS) were laid out in parts of the Baltic Sea, as reported by SVT. 

Swedish and foreign authorities were then able to identify individual surface and underwater vessels, because each vessel has a "fingerprint" - a unique sound.

Important pieces of the puzzle investigation of alien underwater activity.

According to experts SVT Nyheter has been in contact with, SOSUS was put in the "mothbag" when the Cold War ended.

Since then, more modern systems have been developed.

However, it is a state secret if new systems have been deployed or if the older ones have been maintained. 

Activity is detected

The Swedish Armed Forces have confirmed to DN that for two days the navy's ships were near areas where Nord Stream 1 and 2 were later subjected to sabotage.

The navy states on Tuesday that it has not noted increased military activity in the Baltic Sea during the past week.

- There has been a great interest in the Baltic Sea long before, when various nations had their ships in it.

Connected to the gas pipeline itself, it is mostly Swedish and Danish naval vessels that operate.

We have no indication that anyone else would show any interest at this time.

Has Russia advanced its positions?

- I don't comment on what we know and what we don't know, says Jimmie Adamsson, director of communications at the navy.