This study investigates the potential military utility and key priorities of employing extra-large unmanned underwater vehicles (XLUUVs) in the complex and challenging environment of the Baltic Sea. Focusing on payload benefits, technological advancements, and military utility, the research employs a theoretical framework based on concept analysis, systems engineering and military utility. Data is collected and analyzed using a mixed-methods approach including literature review and scenario analysis. The findings suggest that XLUUVs could complement and extend existing defense systems in the Baltic Sea region, demonstrating proficiency in handling diverse missions with factors of flexibility, endurance, adaptability, and modular design. The study highlights the importance of further research and development in areas such as autonomy, communication technologies, and systems integration.