Guardrail Goodbye

An Army Airplane taxis down the runway at Balad Air Base, Iraq after flying a mission in support of operation Iraqi Freedom on July 21, 2006. .(U.S. Air Force photo by Airman First Class Andrew Oquendo) (Not Released)

At fifty years old, the US Army’s Guardrail series of Signals Intelligence (SIGINT) aircraft are looking at a well-deserved retirement.

The Guardrail concept employed a turboprop aircraft, initially Beechcraft’s U-21 based on the company’s King Air turboprop family. From 1983 the army used the RC-12 series based on Beechcraft’s C-12D Heron turboprop . Since then, the RC-12 has been cycled through several incarnations. The RC-12X represents the latest incarnation. The aircraft is deployed at the operational level. It supports the ground force manoeuvre commander by detecting and geolocating radio and radar emissions. The exact frequencies the RC-12X is capable of detecting remain classified. These are most probably wavebands of at least 30 megahertz up to 20 gigahertz. This would allow the aircraft to detect very/ultra high frequency radio signals, and radar signals from red force Weapons Locating Radars (WLRs).

The location of red force units can be determined by detecting and geolocating radio and radar signals. This information can be shared in real time across tactical datalinks allowing commanders to plan and execute their scheme of manoeuvre. A surge in red force radio traffic may mean that manoeuvre is imminent, for example. Meanwhile the collection of electronic intelligence pertaining to WLRs lets artillery determine the location of hostile radars so that these can be made priority targets for fires.


The US Army’s High Accuracy Detection and Exploitation System, or HADES forms the mission system for the Intelligence, Surveillance and Reconnaissance (ISR) aircraft which will replace the RC-12X. Reports state that candidate aircraft include the Boeing 737-800ERX, Gulfstream G-550, Bombardier Global Express and Northrop Grumman RQ-4B Global Hawk.

The HADES payload will include Communications Intelligence (COMINT) and Electronic Intelligence (ELINT) sensors. Reports continue that some of the sensor architecture equipping the HADES mission system has been flown on two Bombardier Challenger-650 test beds. The aircraft, and their mission system, is known as the Aerial Reconnaissance and Targeting Exploitation Multi-Mission Intelligence System, or ARTEMIS.

The US Army revealed their existence in August 2020. Since this announcement, the two aircraft have performed several sorties to the Asia-Pacific and Europe. These aircraft have almost certainly been evaluating the performance of the COMINT and ELINT sensors within the ARTEMIS architecture. A deployment to the Black Sea region in September 2020 is illustrative.


In June, the US Army awarded contracts to L3 and Raytheon for Phase-1 of HADES. Both companies will develop prototype ELINT and COMINT capabilities which for the HADES architecture. This contract should conclude in January 2023.

All the candidate aircraft offer a significant leap over the RC-12X’s current capabilities. Taking the Beechcraft King Air series as a guide, the RC-12 has a range of circa 1,720 nautical miles/nm, a 310 knot (570 kilometres-per-hour) cruising speed and a ceiling of 35,000 feet (10,668 metres). The 737-800ERX has a range of circa 2,935nm (5,436km), a 455 knot (842km/h) cruising speed and a ceiling of 41,000ft (12,497m). The G-550 has a range of 6,750nm (12,500km), a cruising speed of 566 knots (1,049km/h) and a ceiling of 51,000ft (16,000m). The Global Express Global-5000 has a 5,200nm (9,630km) range, a cruising speed of 504 knots (934km/h) and a ceiling of 51,000ft. Finally, the RQ-4B has a 12,299nm (22,780km) range, a cruising speed of 310 knots (570km/h) and a ceiling of 60,000ft (18,000m).

These criteria are important. Range translates into endurance. The longer the range, the longer the aircraft can remain on station. This is vital if the aircraft is to provide the manoeuvre commander continual real-time reports on the situation on the ground derived from the COMINT and ELINT the aircraft gathers.

Likewise speed is important. The quicker the aircraft, the quicker it can deploy. This is particularly relevant if the aircraft is located in the continental United States and needs to rapidly reach Europe or the Asia-Pacific due to a sudden crisis.

Altitude has a similar relevance. The higher you are, the more you can see. Flying at 35,000ft the RC-12 would have a line-of-sight range of 230nm (425km). This is already quite respectable for operational-level SIGINT collection. However, taking either the G-550 or Global-5000 as an example, this increases to 277nm (513km). It is perhaps no surprise that the army is not looking at turboprop platforms for the HADES requirement.


COMINT and ELINT capabilities form one part of the wider HADES architecture.

A spokesperson for the US Army’s Programme Executive Officer for Intelligence, Electronic Warfare and Sensors told Armada that “HADES will carry a variety of SIGINT sensors, synthetic aperture radar/moving target indication radar, cyber, electronic warfare, optronics sensors and air launched effects.”

SIGINT components will be folded into the first increment of HADES, alongside the radar. The spokesperson continued that the open architecture standards at the heart of HADES means that “upgrading, changing or incorporation new sensors will require minimal changes to the aircraft.” This should also keep integration costs manageable during the aircraft’s lifetime.

Reports say that Phase-2 will see the contractors performing additional developmental work on the aircraft’s COMINT/ELINT sensors. The spokesperson stated that, although Phase-2 has been fully funded, its timelines are still to be set: “The government will make that decision based on the amount of development work required as determined by Phase-1, balanced against the desire to rapidly deliver capability to the field.” Although the spokesperson said that there are no firm dates as yet for HADES’ fielding, “we currently plan to deliver HADES to the field as a prototype for soldier evaluation in the 2024/25 timeframe.”

by Dr. Thomas Withington