SIGINT in the Spratlys

Several islands in the Spratly archipelago are believed to be home to PRC signals intelligence facilities including Fiery Cross Reef shown here.

A new authoritative report sheds light on China’s electronic warfare posture in the disputed Spratly Islands.

The People’s Republic of China (PRC) maintains both fixed and mobile Electronic Warfare (EW) assets on Chinese-held territory in the South China Sea, according to J. Michael Dahm, a senior researcher at Johns Hopkins University’s Applied Physics Laboratory. He is the author of a recent report entitled Electronic Warfare and Signals Intelligence: A Survey of Technologies and Capabilities on China’s Military Outposts in the South China Sea.

Operational and strategic-level EW is the preserve of China’s Strategic Support Force (SSF). The SSF manages EW capabilities across the People’s Liberation Army’s (PLA) naval, ground and air forces. Mr. Dahm’s report states that electronic warfare vehicles have been observed from 2018 using satellite imagery on Subi and Mischief reefs in the Spratly Islands. The PRC has occupied several of the Spratly Islands which are claimed by several actors in the South China Sea littoral.

The author adds that as well as these vehicles using prepared concrete pads on these islands and others in the Spratly archipelago occupied by the PRC, it is likely that the vehicles can be hidden or redeployed by sea or air as necessary in times of tension or conflict. The report warns that such an approach “may serve to keep an advancing adversary off balance, unable to anticipate and effectively counter the EW … capabilities dispatched on Chinese outposts.”

Mobile Assets

Mr. Dahm emphasises that one major challenge when researching the PLA’s EW capabilities concerns the electronic warfare order-of-battle, particularly in the land domain: “Comparatively little is known about PLA EW equipment, especially ground-based systems.” He adds that such equipment is rarely seen, usually appearing at military parades, and given an anodyne appellation like “a new type of radar jamming vehicle,” or a “new type of communication jamming vehicle.”

In the open source intelligence world one can at best estimate the capabilities of a particular army EW platform by examining physical characteristics like its antennas. Nonetheless, drawing on published information such as diagrams produced by the China Electronics Technology Group Corporation (CETC), Mr. Dahm shows that the army may have generic capabilities to detect and jam radio and radar emissions across wavebands of two gigahertz/GHz to 18GHz to support ground-based air defence at operational/tactical levels. CETC graphics have shown EW assets being fielded in a regimental-sized deployment.

Fixed installations

Away from the mobile domain, Mr. Dahm’s report makes the important point that High Frequency (HF: three megahertz/MHz to 30MHz) radios used for long-range communications could be employed as HF COMINT collectors.

Likewise, the report observes that a collection of eleven radomes on Fiery Cross Reef in the west of the archipelago might be used to geolocate the source of satellite communications transmissions. The report surmises that this maybe done through Time Difference of Arrival (TDOA) or Frequency Difference of Arrival (FDOA) techniques.

TDOA works be using the microscopic difference in time that the same signal will take to arrive at two separate receivers. The same signal will arrive just slightly earlier at the receiver nearest the transmission than the one further away. By calculating the time difference, it is possible to compute the location of the transmitting radio. FDOA can be used to ascertain the position of a moving target. Doppler Shift is the process by which frequencies rise or lower depending on whether the source of a transmission is moving towards or away from an observer. This is analogous to the rising and falling tone in a police car siren a pedestrian will hear as the car drives towards and away from them. By comparing the Doppler shifts in the same signal taken from two or more observation posts it is possible to compute the position of a moving target. Both TDOA and FDOA are useful techniques these listening stations can employ to locate electromagnetic emitters on ships and aircraft of interest to the PLA.


As Mr. Dahm’s report revealed, HF Communications Intelligence (COMINT) collection sites appear to exist on Mischief Reef in the east of the archipelago. This may be used for the location of HF emitters in conjunction with HF COMINT sites thought to exist on the Chinese mainland and Hainan Island in the South China Sea.

Mischief Reef and Fiery Cross Reef are also thought to be home to Electronic Intelligence (ELINT) collection arrays to collect intelligence on airborne and naval platforms of interest to the PLA. This ELINT could be used to identify specific emitters to help populate the PLA’s electronic orders of battle. It may also help to develop radar jamming waveforms to protect PLA aircraft and ships. Mr. Dahm assesses that the PLA maybe capable of collecting ELINT on airborne radars at ranges of 57 nautical miles/nm (105 kilometres/km) for targets at 1,640 feet (500 metres) to 229nm (425km) for targets flying at 32,800ft (10,000m).


Meia Nouwens, research fellow for Chinese defence policy and military modernisation at the International Institute of Strategic Studies, told Armada that “establishing a SIGINT network” in the archipelago enables the PRC “to expand its maritime domain awareness” and “contributes to the PLA’s strategy to control battlespace information.”

She believes that the PRC is primarily using these SIGINT outposts to collect military signals intelligence, as a response to increased naval activity in the region, particularly freedom of navigation operations lead by the US Navy.

However, Ms. Nouwens does not rule out the use of these facilities for the collection of civilian SIGINT. Nor does she expect the PRC’s interest in these installations to wane any time soon: “Considering the heating up of tensions in the Indo-Pacific, I expect China to continue building SIGINT facilities.” Although she believes Beijing and Washington DC are keen to avoid conflict, from the PRC’s perspective “maintaining an accurate picture of the maritime domain in the region doesn’t just serve long-term strategic goals, but might be important to help avoid miscalculations or misunderstandings.”

by Dr. Thomas Withington