China's magnetic tech can detect US stealth subs: study
Could China's new magnetic wake detection technology mark the end of stealth submarine warfare? Recent Chinese research suggests it might.
This month, South China Morning Post (SCMP) reported that researchers at Northwestern Polytechnical University (NPU) in Xian, China, have unveiled a novel detection method capable of identifying even the stealthiest submarines by tracking their magnetic wakes.
The team, led by Associate Professor Wang Honglei, discovered that the magnetic fields generated by the wakes of submarines, such as the US Seawolf-class, can be detected using airborne magnetometers. This potentially groundbreaking technique exploits the magnetic interactions between seawater ions disturbed by the submarine's motion and the Earth's geomagnetic field.
The study, published in the Journal of Harbin Engineering University in December last year, indicates that speed, depth and submarine dimensions influence the intensity of these magnetic signatures. Unlike traditional acoustic detection methods, magnetic wakes cannot be silenced and leave a persistent trace.
The Chinese research comes after the USS Connecticut grounding in the South China Sea in 2021, which, among other things, highlighted the increasing challenges of stealth operations in contested waters. As China integrates magnetic tracking into its broader 'kill web' of detection technologies, underwater naval warfare may see a transformative shift.
The rapid evolution of submarine detection technologies threatens submarines' traditional stealth and strategic utility, which, in turn, could necessitate innovations in submarine design, countermeasures and operational strategies to maintain their relevance in future conflicts.
Shallow water environments like the Taiwan Strait reduce the effectiveness of traditional sonar systems, while technologies such as Magnetic Anomaly Detection (MAD) introduce new detection capabilities and limitations that complicate submarine tracking.
Magnetic detection offers several advantages over sonar in shallow waters like the Taiwan Strait, which is no more than 150 meters deep. Bo Raskin of the Naval Submarine League states that shallow depths reduce low-frequency sonar effectiveness due to the absence of spherical sound spreading, leading to sound channeling, where energy is absorbed by the seabed and surface reflections.
He adds that towed sonar arrays face challenges in passive detection because long wavelengths of low-frequency sound struggle to propagate in shallow water, while intense bottom reverberation and clutter from the muddy seabed limit the detection of small targets and range.
However, Rajiv Sithiravel and other writers mention in an October 2020 article in the peer-reviewed IEEE Transactions on Aerospace and Electronic Systems journal that airborne MAD has a non-linear problem arising from the complex relationship between a submarine's magnetic signature and motion, complicating accurate tracking and estimation.
Sithiravel and others say the left/right positional ambiguity prevents MAD from distinguishing whether a detected anomaly is to the left or right of the aircraft's flight path without additional maneuvers, such as curved flight paths. In addition, they note that MAD's short detection range makes it more suitable for short-range confirmation rather than long-range detection.
Despite the threat posed by MAD and other sensor technologies, advances in stealth technology and tactics can keep submarines relevant in future conflicts.
A January 2025 article by the Australian Naval Institute says submarines use anechoic tiles, vibration-damping materials, radar-absorbing materials and periodic degaussing to enhance stealth. The article also mentions that submariners employ techniques such as countering detection through noise manipulation and deploying uncrewed underwater vehicles (UUVs).
However, Roger Bradbury and other writers mention in a March 2023 article for The Conversation that advancements in artificial intelligence (AI), sensor technology and underwater communications could potentially render submarines easily detectable and obsolete by the 2050s.
Bradbury and others say these new technologies can identify slight variations in the ocean's physical, chemical, and biological markers and disruptions in the Earth's magnetic field caused by submarines, potentially compromising their stealth and significance in future conflicts.
The US Navy must adapt its submarine design and operational strategies to counter the growing threat of multi-layered detection systems that combine advanced technologies.
Combining airborne MAD with other technologies, such as magnetic wake detection, terahertz-based devices, airborne extremely low-frequency (ELF) radar, and light detection and ranging (LIDAR) satellites, can create a multi-layered detection grid to track US and allied submarines in near real-time.
These advancements have the potential to impact US submarine design and operations significantly. Ryan Neuhard, in a March 2018 article for Georgetown Security Studies Review, says that the US Navy's submarine force faces the challenge of adapting to evolving detection technologies by pursuing several strategies.
Neuhard suggests that upcoming submarine designs might prioritize minimizing sound, magnetic and wake disturbances to evade advanced detection systems, leveraging propulsion, hull design and magnetic cloaking innovations to enhance stealth capabilities.
He adds that the US can improve the protection and effectiveness of its submarines against enemy threats by utilizing defensive measures like jammers and unmanned vehicles while also transitioning them to serve as command centers for autonomous systems.
China's underwater surveillance system in the South China Sea challenges and threatens US submarine operations and has significant strategic implications for regional security and nuclear deterrence.
At the strategic level, China's new submarine detection technologies can help secure the South China Sea as a protected bastion for its nuclear ballistic missile submarines (SSBN), which provide secure nuclear second-strike capability.
In a December 2016 report for the National Maritime Foundation, Dolma Tsering says that China has built an 'Underwater Great Wall' (UGW), a comprehensive underwater sensor network in the South China Sea that combines sensors, sonar, unmanned underwater vehicles and surface ships to monitor both surface and underwater activities in real-time.
Tsering mentions that China's UGW, modeled after the US Cold War-era SOSUS, improves China's submarine detection and tracking capabilities. She notes it directly challenges US operations and requires a reassessment of its undersea strategy, particularly in the strategically important Taiwan Strait.
Further, in a March 2024 report, the South China Sea Strategic Situation Probing Initiative (SCSPI), a Chinese think tank, mentioned that in 2023 at least 11 US nuclear attack submarines (SSN) and two US SSBNs appeared in the South China Sea.
While the report says they aim to 'exert deterrence,' the US SSNs may track China's SSBNs in the South China Sea. Such actions can be destabilizing at a strategic level, as China is highly likely to retaliate against threats targeting its nuclear arsenal.
China's breakthrough in magnetic detection technology may well mark the beginning of the end for submarine stealth. As detection capabilities evolve, future conflicts could see submarines forced to shed their traditional invisibility cloak and adopt new roles, emphasizing long-range precision strikes, drone coordination and command-and-control functions.
The question is not whether submarines will need to adapt—but rather, will they remain relevant in a new era of transparency beneath the waves?
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