Japan is advancing efforts to develop quantum sensor technology for drones aimed at enhancing submarine detection, reflecting increased competition in undersea surveillance across the Indo-Pacific region. The initiative is part of Tokyo’s 2027 defense budget proposal, which includes funding for research into compact quantum magnetic sensors capable of detecting minute variations in magnetic fields associated with submarines.
The sensor technology, expected to be operational by 2031, is planned for integration with low-cost unmanned aerial vehicles that would fly near the sea surface, operating from naval vessels. This approach aligns with Japan's broader strategy to mitigate rising personnel and financial constraints by leveraging uncrewed systems for persistent maritime monitoring.
Experts note that while magnetic sensors have limited detection ranges and are less suited for broad-area searches, their deployment on numerous affordable drones can effectively monitor strategic maritime chokepoints, such as straits through which Chinese submarines must pass to reach the Pacific Ocean. Masashi Murano, a defense analyst at the Hudson Institute, emphasized that unmanned systems could reduce operational costs compared to traditional crewed patrol aircraft while maintaining effective coverage in critical zones.
China has already advanced similar technologies; research teams reported successful sea trials of drone-mounted magnetic sensors last year. Beijing has simultaneously expanded its anti-submarine warfare capabilities, introducing new platforms including the Y-9Q patrol aircraft, Z-20F shipborne helicopters, and Wing Loong X drones designed for sonobuoy deployment. Additionally, China is constructing an extensive sensor network combining satellites, buoys, underwater gliders, and seabed listening arrays—often referred to as an “Underwater Great Wall”—to bolster undersea domain awareness.
These developments coincide with China’s anticipated growth in submarine forces, with the Pentagon projecting the fleet could reach 80 vessels by 2035 as shipbuilding accelerates. In response, the United States and its allies are investing heavily in undersea detection and response technologies. The U.S. Navy has recently evaluated drone systems capable of carrying enhanced sonobuoy payloads, and solicited industry input for Silent Anvil, a compact air-launched torpedo compatible with both crewed and uncrewed platforms.
Under the Aukus security partnership, Australia, the United Kingdom, and the United States have collaborated on developing payloads and support systems for unmanned underwater vehicles. Japan has also engaged in joint exercises and technology testing with these partners, including trials of underwater acoustic communications for autonomous maritime systems. Australia’s upcoming Mogami-class frigates will feature Japanese towed-sonar systems, underscoring deepening cooperation in maritime sensing technology.
Murano characterized the undersea contest as an “accelerating” but asymmetrical dynamic driven by overlapping strategic needs. China’s growing sea-based nuclear deterrent and expanding nuclear-powered attack submarine fleet necessitate advanced undersea surveillance and anti-submarine warfare to protect its assets and extend operational reach beyond the first island chain. For the United States and its allies, effective undersea domain control remains essential because it provides the only persistent operational capability inside China’s long-range weapons engagement zones.
As both sides seek to conceal their own submarine movements while detecting those of their adversaries, the undersea arena is evolving into a complex and critical domain of military competition.