An underwater acoustic network (UAN) represents a communication infrastructure that canoffer the necessary flexibility for continuous monitoring and surveillance of critical infras-tructures located by the sea. Given the current limitation of acoustic-based communicationmethods, a robust implementation of UANs is still an open research field. The FP7 UANproject addressed such a problem, and it reached the integration of a mobile underwatersensor network within a wide-area network, which included above water and underwatersensors, for protection and security. This paper describes some of the main results achievedduring the project. In particular, this work addresses solutions for the upper-layers of theUAN, with focus on the integration of autonomous underwater vehicles (AUVs) as mobilenodes of the network, and on the inclusion of network security mechanisms. The recent at-sea successes that have been demonstrated within the UAN framework are detailed. Resultsare given of the final UAN project demonstration, UAN11, held in the May of 2011, whenan underwater acoustic network composed by four fixed nodes, two autonomous underwa-ter vehicles (AUVs), and one mobile node mounted on the supporting research vessel, wascontinuously operated for one week, and integrated into a global protection system.