Navantia's shipyard in Cartagena, Spain, has accomplished a groundbreaking feat by successfully fitting a Hydrogen-based Air Independent Propulsion System (AIP) into an S-80 class submarine. This achievement, celebrated in the presence of Admiral Aniceto Rosique Nieto, the Spanish National Armament Director, represents the installation of the first third-generation AIP system in a submarine. The implementation of this innovative technology, known as BEST (Bio-Ethanol Stealth Technology) by Navantia, will revolutionize the Spanish Navy's submarine capabilities by allowing prolonged submerged operations compared to conventional diesel-electric submarines. The AIP system operates by utilizing a bioethanol reforming process to produce a Hydrogen-rich stream that powers a fuel cell with pure Oxygen, enabling electrical power generation while maintaining stealth. Notably, Navantia's AIP system eliminates the need for stored hydrogen on board, generating it as required and enhancing operational safety and autonomy. The advanced sensorization of the submarine further reinforces crew safety and operational efficiency. The event also provided attendees with a firsthand view of the S-83 Cosme García submarine's Section 3, housing the AIP equipment, liquid oxygen and bioethanol tanks, and auxiliary systems. This glimpse into the construction process underscored the meticulous work and safety protocols observed in building and integrating this cutting-edge technology. Navantia's successful integration of the AIP system not only sets a new standard in submarine technology but also positions Spain as a leader in innovative naval solutions.