US-made unmanned vessels will monitor maritime activity as part of trial, amid criticism over closer ties with America

Denmark is deploying floating drones on the Baltic Sea to protect undersea infrastructure and bolster maritime surveillance amid the growing threat of hybrid attacks from Russia.

The arrival of Saildrone, a California-based company, has prompted criticism in Denmark over forging tighter bonds with the US in such a sensitive area as digital security.

The backlash comes amid rapidly changing alliances, evolving technology and ongoing tensions between Copenhagen and Washington after Donald Trump threatened to take over Greenland, which is part of the Danish kingdom.

The 10-metre unmanned vessels, known as “saildrones”, resemble sailing boats but are designed solely to collect data. Using onboard AI, saildrones compile data using multiple sensors, cameras and radar to produce a more detailed picture of maritime activity than satellites can provide.