Countries' interest in rearmament in underwater warfare has clearly increased in recent years.
Although information about what happened in the Baltic Sea is scarce, the sabotage of the Nord Stream pipelines has raised the issue of countries' vulnerability to attacks on seabed infrastructure.
- A number of countries are investing in the area, both in technology and research, says Siemon Wezeman, who researches military rearmament at the peace research institute Sipri.
Sabotage like that against Nord Stream 1 and 2 are not commonly occurring acts, according to the experts.
But it is something countries have long been preparing for as long as cables and wires have been laid along the seabed.
- There is an increased interest in both surveillance systems, but also the possibility of, for example, unmanned watercraft, says Siemon Wezeman.
"Must prepare"
This involves, for example, pre-programmed, battery-powered drones that can operate independently in the sea for several months and send data from there.
A technology that has largely been developed by the industry that extracts oil and gas at sea.
Even warfare can be conducted with the help of this technology and in recent years the development of, for example, unmanned defense systems has gained more momentum.
Hans Liwång, docent in military technology at the Norwegian Defense Academy who researches marine systems, points out that countries are facing a transformation of surveillance at sea.
- Countries must continue to prepare for this type of attack, he says.
Do you think it will increase in the future?
- I think it is something we need to be prepared for and that it is something we will see, but not everyday.
At the Royal Institute of Technology, researchers are working on developing technology for unmanned underwater vehicles. See more and hear Hans Liwång tell in the clip above.