<p>Unmanned maritime systems (UMS) can provide important benefits for maritime law enforcement agencies for tasks such as area surveillance and patrolling, especially when they are able to work together as one coordinated system. In this context, this paper proposes a methodology that optimises the coverage of a fleet of UMS, thereby maximising the opportunities for identifying threats. Unlike traditional approaches to maritime coverage optimisation, which are also used, for example, in search and rescue operations when searching for victims at sea, this approach takes into consideration the limited seaworthiness of small UMS, compared with traditional large ships, by incorporating the danger level into the design of the optimiser.</p>