This paper details the development and onboard evaluation of an Unmanned Aerial System (UAS) specifically designed for maritime firefighting and rescue operations on roll-on/roll-off (ro-ro) ships. Emphasizing the use of open hardware and software, the study focuses on the operational practicality and legal fesibility of a UAS prototype. The assessment of the UASs performance is multifaceted, incorporating expert surveys and a SWOT analysis. Key findings demonstrate the significant potential of UASs in augmenting maritime safety and emergency response capabilities. The paper provides insights into broader opportunities for integrating UAS technology in maritime operations, highlighting its role in enhancing the efficiency and effectiveness of critical maritime functions.