Opportunity Knocks

Business jets are increasingly attractive for the SIGINT mission thanks to their altitude and range. Taiwan may decide to use such a platform to satisfy its airborne SIGINT requirement.

Taiwan’s air force may buy new SIGINT aircraft over the next four years.

According to Armada’s records, the Republic of China Air Force (ROCAF) flies a single Lockheed Martin C-130H Hercules tactical turboprop freighter configured for electronic warfare. This aircraft was acquired by the ROCAF in 1991 to gather operational/tactical Signals Intelligence (SIGINT). Tactical SIGINT is also gathered by Thales ASTAC pods equipping the ROCAF’s Dassault Mirage-2000/5EI combat aircraft. Our records show that ten systems were acquired between 1997 and 1998.


Open sources state that the C-130H is outfitted with a payload jointly developed by Lockheed Martin and the Chung Shan Institute of Science and Technology. This is called the Airborne Electronic Surveillance System (AESS). These sources continue that the aircraft can perform electronic attack. It will most probably have two roles: The first will be gathering Electronic Intelligence (ELINT) on hostile ground-based air surveillance, naval surveillance and fire control/ground-controlled interception radars. The second will be collecting Communications Intelligence (COMINT) on hostile surface-to-surface, surface-to-air/air-to-surface and air-to-air radio traffic. The jamming role hints that the C-130H can attack these emitters. Conservatively, the AESS may gather SIGINT across wavebands of two gigahertz/GHz to 18GHz. This may be expanded to frequencies of 500 megahertz/MHz to 40GHz.

The latter may be important due to the People’s Liberation Army’s use of Very/Ultra High Frequency (V/UHF: 133MHz to 144MHz/216MHz to 225MHz and (420MHz to 450MHz/890MHz to 942MHz) ground-based air surveillance radars. These are widely used by the People’s Liberation Army Air Force (PLAAF). V/UHF radars have relatively long wavelengths. This helps them detect airborne targets with low radar cross sections.

VHF Radar

News has come to light in recent years regarding Chinese V/UHF radar. A report entitled In-Depth: Subi Reef Counter-Stealth Radar written by J. Michael Dahm and published by Johns Hopkins University’s Applied Physics Laboratory gives some insight. For example, the PLAAF is thought to deploy a VHF radar on Subi Reef in the South China Sea’s Spratly Islands. The People’s Republic of China has a disputed claim on the Spratly Island’s sovereignty.

Mr. Dahm states that the radar is designated a Synthetic Impulse and Aperture Radar (SIAR) by the PLAAF. The Spratly Islands are 713 nautical miles/nm (1,320 kilometres/km) almost due south of Hong Kong. The SIAR would provide the PLAAF early warning of incoming aircraft.

The SIAR is not the only VHF ground-based air surveillance radar in PLAAF service. Other systems like the China Electronics Technology Group Corporation’s JY-27A have also been identified. These are thought to be in service on the Chinese mainland.

Any future confrontation between the PRC and a US-led coalition would probably involve low RCS aircraft and weapons. These would be employed during initial air strikes. One can see why the detection of such potential threats is of high importance to the PLAAF.

The Spratly Islands are potentially outside any putative PRC/Taiwan theatre of operations. Yet one cannot dismiss the fact that similar VHF radars maybe deployed by the People’s Republic of China in coastal areas facing Taiwan. They may also be positioned in vicinity of expected ROCAF ingress and egress routes for strategic or operational targets. Detecting and engaging  VHF radars will thus be imperative.

A second motivation for the new SIGINT aircraft is the recent upgrade of the ROCAF’s air defence suppression capabilities. In 2020 Taiwan purchased 50 Northrop Grumman AGM-88E AARGM (Advanced Anti-Radiation Guided Missile) rounds. These will equip the ROCAF’s General Dynamics/Lockheed Martin F-16 Fighting Falcon series jets. The new airborne SIGINT platform will collect relevant ELINT to target PLAAF radars.


It seems likely Taiwan would procure a business jet to fulfill this requirement. Such platforms give a major advantage regarding detection range. The current C-130H will have an emitter detection range of circa 404nm (748km). A Gulfstream G-550 business jet has a ceiling of 51,000 feet (15,554 metres). This would increase the emitter detection range to 502nm (930km). The aircraft could thus maintain good stand-off distances regarding PLAAF radars.

Armada expects the ROCAF to procure at least two new SIGINT aircraft. We expect up to $5 million could be spent on airborne SIGINT systems to equip them. Given that Taiwan is taking delivery of its new AGM-88Es, we expect the SIGINT aircraft procurement to occur by 2025.

by Dr. Thomas Withington