On 15 April 2026, the Sierra Nevada Corporation (SNC) announced the completion of testing and validation of the ‘Army Theatre-Level High Altitude Expeditionary next Airborne-Signals’ (ATHENA-S) Signals Intelligence (SIGINT) platform, with the US Army now considering the system operational. SNC stated that the completion of the trials work “confirms the aircraft’s design, mission systems integration and operational performance, marking the transition… to operational service in support of US Army mission requirements.”

The two modified Bombardier Global 6500 (G6500) aircraft have since entered operational service as ‘contractor-owned/contractor-operated’ (COCO) assets, available for tasking by the US Army. The first ATHENA-S deployment began promptly, with the aircraft reportedly arriving in the Philippines shortly after, in support of US Indo-Pacific Command (USINDOPACOM).

These aircraft join two further modified Global Express airframes dubbed ‘ATHENA-Radar’ (ATHENA-R), developed by L3 Harris and MAG Aerospace. Two ATHENA-R aircraft are already operational and have been operating within the USINDOPACOM area of responsibility from South Korea since February 2025.

Unlike most COCO intelligence, surveillance, and reconnaissance (ISR) platforms, which are developed independently by industry and offered to customers as services, the two ATHENA variants form part of the US Army’s wider efforts to recapitalise its airborne ISR capability. The aircraft serve simultaneously as operational assets, providing in-theatre intelligence gathering capabilities to the US Army, as well as demonstrators and testbeds in support of the High-Altitude Detection System (HADES) programme.

The two ATHENA-S aircraft join a growing cadre of contractor-owned-and-operated ISR platforms supporting this program across various intelligence disciplines. The concept of operations has largely focused on fielding capabilities in support of real-world missions to inform the development of future systems, sensors, and concepts of operation that will be integrated into what will eventually become the ME-11B HADES, an all-encompassing multi-intelligence platform that will combine both SIGINT and Radar capabilities.

Under HADES, the service currently projects that it will operate a fleet of up to 11 ME-11B aircraft, which will also be based on the G6500. These aircraft will be developed by SNC and owned, and operated by the US Army. It should be noted that the HADES aircraft appear set to be new-build rather than conversions from predecessors, as evidenced by the US Army issuing a request for information (RFI) in January 2026, pertaining to the acquisition of up to 11 G6500 airframes for conversion to the HADES standard.

Within the group of predecessors to HADES, the two ATHENA variants are the final development stage before the full HADES capability enters service, which is projected for 2027. In the meantime, the US Army announced it had completed the withdrawal of its entire legacy ISR fleet in December 2025. In the interim, the HADES predecessor platforms have been, and continue to support US Army intelligence gathering across the European and Pacific theatres, as detailed in Table 1.

HADES: A quick overview

At large, HADES forms the conventional airborne ISR pillar within the US Army’s ‘Multi Domain Sensing System,’ (MDSS) which includes a variety of sensor types across air, space and cyberspace. The rationale behind the HADES platform aligns with broader trends and narratives surrounding ‘peer-conflict.’ This includes the need for vulnerable ISR aircraft to be responsive, stand off from anti-aircraft systems, as well as higher speeds, long ranges and endurance, giving them extended time ‘on-station’, as well as the ability to deploy, and/or reach an area of interest more quickly.

Until now, the US Army’s airborne-ISR (A-ISR) capabilities have been a combination of Cold War platforms and those optimised for tactical ISR in support of counterterrorism and irregular warfare operations. These aircraft have spanned the Beechcraft King Air series, as well as De Havilland Canada Dash-7 and Dash-8 variants. In short, these turboprop aircraft have low ceilings, limiting their detection ranges, and are relatively slow, leaving them suited to stand-in operations in permissive environments rather than the operational parameters of a peer conflict.

As such, HADES, to paraphrase director of Strategy and Transformation within the US Army G2 (intelligence staff) Andrew Evans, will “fly faster, higher and further” than the legacy turboprop fleet. In principle, higher operating altitudes provide greater line of sight, allowing aircraft to sit farther away from surface-to-air threats. Meanwhile, the greater range and speed should improve responsiveness, whether in deploying between theatres or from forward bases farther from the area of interest.

A taste of HADES

ATHENA-S represents the fourth platform on the road to HADES so far, but it is perhaps the most significant. SNC won the contract to convert the full ME-11B aircraft in 2024, with the company stating it intended to use approximately 90% of the ATHENA-S suite on its final HADES platform, making it the most comprehensive system on the road to the final offering so far. Specific details around sensors and capabilities remain unavailable, though the aircraft itself is built around SNC’s ‘Rapidly Configurable to Any Mission’ (RAPCON-X) open architecture.

Using the aircraft’s basic flight characteristics, we can quickly get an idea of how this capability will advance the US Army’s airborne Signals Intelligence-gathering capability. Previously, the service’s primary airborne SIGINT asset was the RC-12 Guardrail Common Sensor (GRCS), based on the Beechcraft King Air 200, and the first variants entered service during the 1970s.

Based on RAPCON-X’s specifications, ATHENA-S offers approximately 14 hours of endurance, operates at altitudes of, or exceeding 45,000 feet (13,716 m), and has a range of approximately 6,000 nautical miles (11,112 km). By contrast, the RC-12 was limited to between 5 and 6 hours of endurance, a range of approximately 1,200 nautical miles (2,222 km) and operating altitudes between 20,000 and 30,000 feet (6,096 and 9,144 m). Using aircraft with similar characteristics, it becomes clear how increasing altitude will increase the aircraft’s detection range and overall sensing capabilities.

The concept of operations also represents a substantial change between the two platforms, as the GRCS operated as part of a system, rather than as a standalone asset. This required at least two aircraft operating in complementary orbits to conduct direction finding, while the collected data was passed to a ground-based processing station.

By contrast, ATHENA-S, and the other platforms involved in the development of HADES, all deliver these capabilities from a single aircraft. RAPCON-X, for instance, has a configurable cabin that can accommodate at least four operator positions. Of course, most of the Army’s other legacy ISR platforms did possess onboard operators; however, the RC-12 represents the closest comparison in mission, as it was developed with peer-adversaries in mind during the Cold War. The pivot towards a single platform, therefore, reduces the additional vulnerabilities posed by operating multiple airborne assets and additional ground infrastructure.

SNC’s press release also highlighted the “[artificial intelligence (AI)/machine learning (ML)] enabled processing,” which in the context of SIGINT should allow the automated detection and classification of emitters based on existing Technical Electronic Intelligence data. This will make it much simpler to decipher the electronic order of battle in increasingly congested electromagnetic environments, reducing decision-making cycles, especially if the aircraft is operating in direct conjunction with field units.

Looking ahead

Short of its inherent ‘try-before-you-buy’ benefit, the family of COCO trials aircraft, that includes the two ATHENA variants, has been pivotal to sustaining the US Army’s ISR ecosystem as its legacy systems have been rapidly phased out, alongside informing the HADES aircraft development.

The deployment of the ARTEMIS ELINT aircraft to Eastern Europe, for instance, has continued following the withdrawal of the RC-12X Guardrails that were deployed to Lithuania until their withdrawal in 2023. This has allowed the US Army to retain its ability to monitor key centres of gravity along Europe’s Eastern Flank without yet having formally replaced the now retired Guardrail fleet.

However, ambiguity around the future fleet size of the ME-11B capability does come into question. It has been suggested that this could be as low as six aircraft, and even at 11, it is a significant reduction from the vast turboprop fleet previously operated. Currently, the small fleet of approximately seven demonstrator aircraft is almost entirely deployed across different theatres, suggesting that such a small fleet would constitute a significant loss of mass. Though, we should acknowledge that HADES is only one pillar within the MDSS, and other cross-domain capabilities will of course contribute to a holistic ISR picture.

It is also worth considering whether the wholesale retirement of the legacy fleet could create capability gaps at the lower end. Many of these platforms were optimised for low-intensity and other irregular warfare operations in permissive airspace. Firstly, these missions will not entirely disappear, in spite of the transition to peer-conflict, while secondly, lower operating costs make them well suited to persistent, sub-threshold monitoring.

Like all other operators, the US Army has had to prioritise what it feels its primary focus should be. It is therefore without doubt that the introduction of ATHENA-S represents a critical step forward to achieving its goals in providing high-end, standoff SIGINT in a peer-threat environment, beyond the capabilities of the GRCS.

The COCO model is certainly facilitating a much faster and effective transition, as well, avoiding large capability gaps as the service continues to advance towards HADES. It is this model that, in the future, could well augment new capabilities at the lower end, as several companies now offer these niche capabilities as a service.