NEREUS consists in designing adaptive opto-acoustic communication systems for mobile delay and disruption resilience networks made of the Uncrewed Underwater and Surface Vehicles. Flexible task-dependent security is integrated by design in the Marine Unmanned Systems. Security technology will be developed to adapt both to the task requirements and to the available communication performance constraints. Underwater vehicles will implement stealth navigation and positioning systems to be able to activate the available communication systems providing the needed communication capability. The developed solutions will be verified in real conditions in Trondheim fjord and in the North Sea test facilities available in the Netherlands.