Spanish shipyard Navantia in Cartagena has successfully installed its Hydrogen-based Air Independent Propulsion System (AIP) in the third S80 class submarine, allowing it to remain submerged underwater for nearly 21 days. The AIP system has undergone extensive testing and offers a substantial improvement over traditional battery-charging submarines, providing enhanced stealth capabilities for naval operations. The Indian Navy, following a successful field evaluation trial, is looking to procure six submarines with the AIP system under Project 75 India (P75I). Navantia's AIP technology, named BEST (Bio Ethanol Stealth Technology), utilizes bioethanol as a fuel source. This not only makes the system environmentally friendly but also eliminates the need for specialized hydrogen-refuelling systems, making refueling easier at any port globally. The technology is designed to produce hydrogen on demand rather than storing it onboard, ensuring safety. Navantia is also considering India as a potential second manufacturing base to produce submarines for Asian clients, with discussions underway with Larsen and Toubro (L&T). This strategic partnership aligns with India's goal of enhancing its submarine-building capabilities and fostering international collaborations in defense manufacturing. The initiative signifies a significant leap in naval defense technology and sustainability practices, marking a positive step towards innovation and strategic partnerships in the defense sector.