Navantia recently celebrated a significant achievement with the completion of the first hydrogen-based air-independent propulsion (AIP) system installation on a Spanish Navy S-80 Plus-class submarine in Cartagena, Spain. The ceremony, held at Navantia's shipyard, marked the successful integration of the Bio-Ethanol Stealth Technology (BEST) AIP system, enabling the submarines to operate submerged for extended periods. The BEST-AIP system, a third-generation technology, utilizes bioethanol reforming to generate hydrogen on board, eliminating the need for stored hydrogen. This innovation, a collaborative effort between Navantia, the Spanish Navy, Collins Aerospace, Abengoa, and Bionet, offers enhanced submarine capabilities while emphasizing the use of bioethanol as a renewable and easily accessible hydrogen source. Comprising a bioethanol reformer, a militarized proton exchange membrane fuel cell, and a carbon dioxide disposal system, the BEST-AIP solution ensures efficient and sustainable submarine propulsion. Navantia's strategic choice of bioethanol as a fuel is justified by its global availability, cost-effectiveness, safety profile, and minimal infrastructure requirements. The successful implementation of the hydrogen-based AIP system reflects Navantia's commitment to technological innovation and environmental sustainability in naval operations.