###### Abstract  
As maritime and military missions become more and more complex and multifactorial over the years, there has been a high interest in the research and development of (autonomous) unmanned underwater vehicles (UUVs). Latest efforts concern the modeling and simulation of UUVs' collaboration in swarm formations, towards obtaining deeper insights related to the critical issues of cybersecurity and interoperability. The research topics, which are constantly emerging in this domain, are closely related to the communication, interoperability, and secure operation of UUVs, as well as to the volume, velocity, variety, and veracity of data transmitted in low bit-rate due to the medium, i.e., the water. This paper reports on specific research topics in the domain of UUVs, emphasizing interoperability and cybersecurity in swarms of UUVs in a military/search-and-rescue setting. The goal of this work is two-fold: a) to review existing methods and tools of semantic modeling and simulation for cybersecurity and interoperability on the Internet of Underwater Things (IoUT), b) to highlight open issues and challenges, towards developing a novel simulation approach to effectively support critical and life-saving decision-making of commanders of military and search-and-rescue operations. IoUT; UUVs; swarm; interoperability; semantics; cybersecurity; simulation +
Footnote †: journal: _Future Internet_**2023**, _15_, 11. [[https://doi.org/10](https://doi.org/10)]([https://doi.org/10](https://doi.org/10)). them, with the most fundamental being the human factor. UUVs/AUVs demonstrate some form of intelligence, planning their own path, without exclusively depending on humans, acting completely autonomously most of the time. ROVs, on the other hand, depend on a remote human operator, and, as a result, many restrictions in their usage are emerging. Both UUVs/AUVs and ROVs, usually operate in an underwater wireless sensor network (UWSN). This type of network supports the monitoring of the aquatic environment and the wireless bidirectional transmission of data between users, i.e., underwater vehicles. This paper's focus is on UUVs/AUVs. UUVs/AUVs are considered today a powerful scientific and military \"tool\" which, when operating in swarm formations, achieve tremendous goals. A swarm of UUVs concerns multiple UUVs that can interoperate, communicate, and behave as a unit. Ideally, one of the UUVs is the leader, having the main decision-making role. Several sub-groups with leaders could also exist. Every unit in the swarm should have the permission and ability to take leadership in situations where the leader is unable to operate efficiently (for any reason, e.g., circuits' damage). The operation of UUVs in a swarm is a powerful platform that provides huge capabilities towards a successful operation (military, scientific, other), even in risky and hazardous settings, putting aside any ethical doubts of a human (e.g., military commander, chief scientist), especially when the full-autonomous decision-making loop for the leader is achieved. Semantic knowledge and ontologies are key solutions to achieve successful interoperability in a swarm of UUVs, ensuring all the above requirements. Whatever the mission/operation, UUVs/AUVs can support it efficiently, either in civilian or in naval SAR and military operations. For example, the AUV A18D of ECA GROUP ([[https://www.ecagroup.com/en/solutions/a18-d-auv-autonomous-under](https://www.ecagroup.com/en/solutions/a18-d-auv-autonomous-under)]([https://www.ecagroup.com/en/solutions/a18-d-auv-autonomous-under](https://www.ecagroup.com/en/solutions/a18-d-auv-autonomous-under)) water-vehicle, accessed on 20 November 2022) achieved the precise mapping of the seabed at a depth of 3000 m in the strong currents of Atlantic; it also efficiently detected various debris and wrecks [1]. Furthermore, AUVs supported a huge operation surrounding a plane crash (Air France Flight 447), discovering pieces of the plane and its \"black box\" with side-scan sonar [2].