The underwater domain has evolved into a critical arena for hybrid warfare, where national security is tied to the protection of vital infrastructure like submarine cables and gas pipelines. Disruptions could have severe economic impacts, prompting a global market for underwater defense estimated at €50 billion annually. Companies like Fincantieri Underwater Hub are developing advanced systems like the DEEP system, which utilizes drones and AI for threat detection and mitigation. Emerging technologies, including quantum sensors and underwater wireless networks, are enhancing defense capabilities. Geopolitical tensions are leading to fragmented digital infrastructures, potentially creating separate ecosystems.