China tests airborne coil array that may detect submarines
Synopsis
China has flight-tested a helicopter-towed electromagnetic coil array capable of sensing conductive objects beneath water — a civilian geophysics tool with unmistakable dual-use potential that could challenge the stealth advantage of nuclear submarines in contested Pacific waters.
Key Takeaways
China conducted a test flight of an Airborne Transient Electromagnetic (ATEM) detection system at an undisclosed site, towing a large coil array beneath a helicopter.
Results were published in Acta Aeronautica et Astronautica Sinica on April 25 , led by associate professor Fu Jingcheng of Beihang University and the Chinese Academy of Sciences' Institute of Geology and Geophysics .
The system fires electromagnetic pulses that penetrate ground or water and detects secondary fields from conductive objects, revealing their presence and depth.
The key engineering advance is stabilising a multi-coil airborne array during flight — a problem that had previously limited practical use of such systems.
While framed as a geophysical survey tool, the technology has clear dual-use potential for detecting submarines, including nuclear-armed vessels operating in the South China Sea and Pacific .
The publication in an open journal is seen by analysts as a deliberate signal of capability amid intensifying US – China strategic competition.
China has conducted a test flight of a large-scale Airborne Transient Electromagnetic (ATEM) detection system, towing a kite-like array of massive coils beneath a helicopter at an undisclosed site. Results of the trial were published in the peer-reviewed Chinese journal Acta Aeronautica et Astronautica Sinica on April 25, raising questions about the technology's potential military applications — including the detection of nuclear submarines.
How the technology works
The ATEM system operates by firing a powerful electrical pulse through a giant transmitter coil, generating a brief but intense electromagnetic field capable of penetrating the ground or water below. When the pulse is switched off, the field induces tiny, decaying eddy currents in any conductive material it encounters, which in turn produce a secondary magnetic field detected by a receiver coil.
By analysing the strength and decay rate of that secondary signal, scientists can determine the presence, composition, and depth of submerged or buried conductive objects. The technique has established civilian applications in mineral and geological surveys, but its ability to sense objects beneath water has drawn scrutiny from defence analysts.
The engineering breakthrough
The study was led by associate professor Fu Jingcheng of Beihang University and the Chinese Academy of Sciences' Institute of Geology and Geophysics. According to the published paper, the research solves a formidable engineering challenge: keeping a complex, multi-coil airborne system perfectly stable during flight — a prerequisite for reliable geophysical survey data.
Maintaining coil geometry and orientation at altitude, where wind turbulence and rotor wash can distort readings, had previously limited the operational accuracy of such systems. The team's solution reportedly makes large-scale airborne electromagnetic surveys significantly more practical.
Why it matters: the submarine detection question
Conventional submarine detection relies on Magnetic Anomaly Detection (MAD) sensors and sonar arrays. The ATEM approach is distinct — its active electromagnetic pulse can, in principle, penetrate seawater to a useful depth, potentially complementing or extending existing detection capabilities. While the paper frames the work as geophysical research, the dual-use implications are significant given ongoing strategic competition in the South China Sea and the broader Pacific.
Nuclear submarines are among the hardest military assets to track precisely because they avoid surface and air exposure. Any technology that credibly narrows that advantage would represent a material shift in undersea warfare dynamics.
Competitive backdrop
The United States and its allies have invested heavily in anti-submarine warfare (ASW) capabilities, including airborne MAD systems deployed on maritime patrol aircraft. China's advancement in airborne electromagnetic detection adds a new dimension to that competition, particularly as tensions over Taiwan and freedom-of-navigation operations in the South China Sea remain elevated.
Industry analysts note that publishing the findings in an open academic journal — rather than classifying them — suggests Beijing may be signalling a capability threshold as much as advancing the underlying science.
What's next
The test flight represents an early-stage validation rather than an operational system. Further trials would be needed to determine effective detection depth against submarine-sized metallic objects in open-ocean conditions. How quickly China moves from geophysical proof-of-concept to a deployable military sensor will be the critical variable to watch.
Point of View
But the deeper story is that electromagnetic detection sidesteps the acoustic signature problem that has defined submarine stealth for decades. If ATEM can be scaled and hardened for open-ocean use, it would erode one of the most reliable sanctuaries available to US and allied nuclear forces. The pace of transition from academic paper to operational sensor — not the test flight itself — is what defence planners in Washington, Canberra, and Tokyo should be tracking.
NationPress
25 Jul 2026
Frequently Asked Questions
What is China's Airborne Transient Electromagnetic (ATEM) detection system?
ATEM is a helicopter-towed array of large electromagnetic coils that fires powerful electrical pulses into the ground or water below and detects the secondary magnetic fields produced by conductive objects. It can reveal the presence, type, and depth of buried or submerged targets. The system has established uses in mineral exploration and geological surveys.
Can the ATEM system actually detect nuclear submarines?
The technology is theoretically capable of detecting large metallic objects beneath water, which includes submarines, but the published research does not claim operational submarine-detection capability. The test focused on solving the engineering problem of keeping the coil array stable during flight. Further trials in open-ocean conditions against submarine-sized targets would be required to assess real-world effectiveness.
Who led the research and where was it published?
The study was led by associate professor Fu Jingcheng of Beihang University and the Chinese Academy of Sciences' Institute of Geology and Geophysics . It was published in the Chinese peer-reviewed journal Acta Aeronautica et Astronautica Sinica on April 25 .
How is ATEM different from existing submarine detection methods like MAD or sonar?
Traditional Magnetic Anomaly Detection (MAD) passively senses distortions in Earth's magnetic field caused by a submarine's metal hull, while sonar uses acoustic pulses. ATEM actively fires electromagnetic pulses that can penetrate water to detect conductive objects, potentially offering a complementary detection layer that does not depend on acoustic signatures — the primary stealth advantage of modern submarines.
Why does this matter for US-China competition in the South China Sea?
Undersea stealth is central to nuclear deterrence and power projection in the Indo-Pacific . If China develops a reliable airborne system for detecting submarines, it would directly challenge the operational security of US and allied submarine fleets operating in the South China Sea and Pacific . The open publication of the research is widely interpreted as a deliberate signal of advancing capability.
