Constantly under power, wind or sun, always wide awake, hear and see everything, under and above water, but never seasick! The Danish Ministry of Defence has put four Voyager naval drones from US manufacturer Saildrone into service in order to detect and fend off potential espionage and sabotage attempts on critical infrastructure at an early stage. The autonomous vehicles are electrically powered by wind and solar energy, allowing them to operate cost-effectively at sea for months without direct intervention. Autonomous control and navigation systems are installed to carry out autonomous military surveillance missions. Optical, acoustic and infrared sensors, including radar and sonar, provide data that can be aggregated into a complex picture of the surface and underwater situation using artificial intelligence and machine learning. In this way, potentially threatening behaviour at sea can be detected at an early stage and transmitted to the base for further action. However, they are not armed, so that other units of state authorities must be deployed for enforcement if necessary. The 10-metre-long sailing drones are based at the small ferry port of Köge in the bay of the same name directly south of Copenhagen, at the mouth of the Öresund.