Unusual US flights may signal secret HACM hypersonic missile testing in Australia
New Testing Theater Down Under
Bottom Line Up Front
The U.S. Air Force's Hypersonic Attack Cruise Missile — a Raytheon/Northrop Grumman scramjet weapon intended to reach initial operational capability in FY2027 — appears to have begun flight testing at Australia's Woomera Range Complex this week under the bilateral SCIFiRE program, consistent with FY2026 budget plans. The program carries an estimated $2 billion development price tag, faces a reduced test schedule of just five flights (down from seven), and is absorbing projected cost overruns that prompted the Air Force to simultaneously resurrect the rival AGM-183A ARRW boost-glide missile. Australia's RAAF is integrating HACM onto its F/A-18F Super Hornets and will serve as a critical test range partner throughout the campaign, operating under AUKUS Pillar II framework.
Key Numbers:
- Mach 5+Cruise Speed (to Mach 8 design goal)
- ~1,900 km Operational Range
- $802 M FY2026 Budget Request
- ~$2BTotal Development Cost Estimate
- 5 Remaining Flight Tests Before IOC
- FY2027 Planned IOC
Something unusual happened over the South Australian outback on the weekend of March 22–23, 2026. A modified Gulfstream G550 intelligence-collection aircraft registered to the U.S. Missile Defense Agency — tail number N551HA — transited from Hawaii through Guam to RAAF Base Edinburgh near Adelaide, then began repeated high-altitude passes along the boundary of the Woomera Protected Area, one of the world's largest restricted overland test ranges at more than 120,000 square kilometers. Flying in coordinated tandem was an Australian P-8A Poseidon maritime patrol aircraft. Neither government confirmed or denied whether a weapon had been launched. Both declined detailed comment.
To analysts who have tracked the Hypersonic Attack Cruise Missile program, the pattern was familiar. The loitering flight profile of a telemetry-collection platform, the concurrent use of a sensor-equipped maritime patrol aircraft for overland surveillance coverage, the deployment of MDA personnel to Edinburgh ahead of "sensitive" operations at Woomera — all are consistent with the instrumentation and range-clearance procedures associated with a hypersonic flight trial. Sources confirmed to The Nightly, the Australian publication that first reported the activity, that the flights were linked to work under the SCIFiRE program — the Southern Cross Integrated Flight Research Experiment — the bilateral U.S.-Australian framework that has underpinned HACM's development and now provides the test infrastructure the U.S. cannot replicate at home.
A Weapon Born From Fifteen Years of Scramjet Research
HACM did not emerge from a clean sheet. It is the operational successor to DARPA's Hypersonic Air-breathing Weapon Concept (HAWC), which achieved successful powered hypersonic flights in March and July 2022 and January 2023 using a Raytheon/Northrop Grumman design. SCIFiRE itself officially launched in November 2020 as an outgrowth of the 2007 Hypersonic International Flight Research Experimentation (HIFiRE) program, which the same U.S.-Australian partnership used to explore scramjet flight dynamics and reach Mach 8.
In December 2021 the Air Force approved HACM as a Middle-Tier Acquisition rapid prototyping program, mandating completion within five years. Raytheon received a $985 million cost-plus fixed-fee contract in September 2022 to cover design, integration, qualification, and flight testing of all-up rounds. A subsequent $407 million award in 2023 for capability enhancements brought the total contract value to approximately $1.4 billion. Northrop Grumman is responsible for the scramjet propulsion system.
Under the SCIFiRE partnership, three manufacturers — Boeing, Lockheed Martin, and Raytheon — submitted competing preliminary designs. Raytheon was competitively selected in September 2022. "Under the SCIFiRE partnership with Australia that was established in 2021, HACM engaged three weapons manufacturers, executed three preliminary design reviews, and competitively down-selected to Raytheon in September 2022," Dr. James Weber, the Pentagon's Principal Director for Hypersonics, told Congress in written testimony. "This program recently conducted wind tunnel testing of the all-up round and static fire ground tests for its new rocket motor."
How HACM Works
HACM is a two-stage weapon. At launch from a tactical aircraft, a solid rocket booster accelerates the missile to above Mach 4, sufficient to sustain combustion in the Northrop Grumman scramjet engine that then takes over for the cruise and terminal phases. Unlike boost-glide designs such as the AGM-183A ARRW or the Army's Long-Range Hypersonic Weapon (Dark Eagle), HACM sustains powered flight throughout its trajectory, drawing atmospheric oxygen for combustion rather than carrying oxidizer — an arrangement that reduces mass and enables the approximately 1,900-kilometer range the Air Force specifies for the system.
Speeds of Mach 5 to potentially Mach 8 — corresponding to roughly 6,200–9,800 km/h — characterize the cruise phase. The missile's compact form factor, designed to be carried on F-15E Strike Eagles, F/A-18F Super Hornets, EA-18G Growlers, F-35A Lightning IIs, and potentially the P-8A Poseidon, represents a deliberate departure from larger platform-constrained hypersonic weapons. A B-52 could potentially carry 20 or more HACMs; a B-1 could accommodate up to 36, according to Air Force statements to Congress. This flexibility is central to the program's rationale: dispersing hypersonic strike capacity across diverse platforms rather than concentrating it on bombers.
The engineering challenges are formidable. Sustained scramjet combustion — compressing supersonic airflow, mixing fuel, and maintaining ignition within milliseconds — demands advanced thermal protection as aerodynamic heating drives surface temperatures to extreme levels. The challenge is roughly analogous to the thermal environment of the SR-71 Blackbird, but sustained at operational altitudes with precision guidance requirements that did not exist in the reconnaissance era.
Schedule Slippage and Cost Growth
By June 2025, the Government Accountability Office's annual assessment of major defense programs delivered a straightforward verdict: HACM is "behind schedule." The preliminary design review originally planned for March 2024 was deferred by six months to September 2024 because, as program officials explained to GAO, more time was needed to finalize the hardware design. A follow-on review to certify the fully operational configuration for final flight tests was rescheduled to sometime in 2025.
The cascading effect was significant. The Air Force will have time to conduct only five flight tests before declaring the weapon operational — a reduction from the original plan of seven. Air Force officials told the GAO that five flights would still be sufficient to establish confidence in the missile ahead of a rapid fielding decision. A validation review covering the final configuration was expected to precede the last test flights.
Cost growth has tracked alongside the schedule pressure. The program's development cost as of January 2025 was estimated at close to $2 billion — a two percent increase from the previous year's assessment of $1.9 billion. More significantly, GAO reported that Raytheon is "projecting that it will significantly exceed its cost baseline." Air Force officials told the watchdog that eliminating two flight tests could produce savings, but the FY2026 budget request — which funded HACM at $802 million, up from $466.7 million appropriated in FY2025 — suggests the Air Force chose to preserve the test campaign rather than cut flights to control costs.
An Air Force spokesperson declined to comment on the specific status of HACM development citing "enhanced program security measures." Raytheon did not respond to press inquiries. That reticence reflects a deliberate classification posture: the service announced in early 2025 that it would withhold information on its hypersonics programs for security reasons.
ARRW Resurrection — A Hedge Against HACM Delays
The Air Force's FY2026 budget request included a development not widely anticipated: $387.1 million to resurrect the AGM-183A Air-Launched Rapid Response Weapon, a Lockheed Martin boost-glide missile previously deemed a lower priority than HACM. The service had requested no ARRW funding in FY2025 after the program endured a rocky test campaign that included a failed all-up-round test in 2023.
Air Force Chief of Staff Gen. David Allvin told House lawmakers on June 5, 2025 that the service would pursue two distinct hypersonic programs. "One is a larger form factor that is more strategic, long-range, that we have already tested several times — it's called ARRW. The other is HACM," he said. Air Force Secretary Troy Meink told the same hearing: "We've got to be able to buy more than 10. We've got a big focus on achieving scale and low cost for the weapons." The timing of ARRW's restoration — concurrent with HACM's delayed first flight — was widely interpreted as a hedge, ensuring the Air Force maintains a hypersonic strike path even if HACM's development continues to encounter friction.
The two weapons are structurally complementary. ARRW, boosted to hypersonic speed by an ATACMS rocket before gliding to its target, is larger and must be carried by bombers. HACM's air-breathing configuration gives it longer range for its size and the ability to fly "vastly different trajectories," as Air Force budget documents describe it — a reference to the powered maneuverability that distinguishes scramjet cruise from boost-glide.
Woomera: Why America Tests in Australia
The United States faces a structural constraint that the Woomera partnership directly addresses: there is no domestic test range offering the overland distance, remoteness, and airspace freedom required for full-envelope hypersonic trials. GAO stated explicitly that "test range availability and limitations in the U.S. have been an issue for hypersonic programs" and identified the SCIFiRE/HACM integration as the mechanism to alleviate it.
Australia's Woomera Protected Area covers over 120,000 square kilometers of arid terrain in South Australia. Its restricted airspace allows unimpeded flight paths exceeding 1,000 kilometers — a near-requirement for a weapon with HACM's stated range. The range infrastructure includes radar tracking stations, telemetry receivers, and optical instrumentation capable of collecting aerodynamic and thermal data from high-speed flight. Woomera has supported joint U.S.-Australian hypersonic research since the HIFiRE program, providing the instrumented overland corridor that no U.S. range can duplicate.
Australia's commitment extends beyond range access. The Australian Defence Department confirmed that the RAAF is integrating HACM onto its fleet of 24 F/A-18F Super Hornets, consistent with the 2024 Integrated Investment Plan's intent to equip those aircraft with a hypersonic weapon ahead of their planned retirement around 2040. "Through the SCIFiRE agreement, the U.S. and Australia continue to collaborate on HACM design and development, including efforts to integrate HACM on RAAF F/A-18Fs and using Australian test infrastructure for flight tests," a Defence spokesperson told Australian Defence Magazine. In Australian service, HACM will be the first hypersonic weapon to be operated in the Oceania region.
Australia's defence investment in the broader hypersonic domain is substantial. The 2020 Defence Strategic Update included funding of $6 billion to $9 billion for high-speed long-range strike research out to 2040. In November 2024, the three AUKUS partners — the United States, United Kingdom, and Australia — signed the Hypersonic Flight Test and Experimentation (HyFliTE) Project Arrangement under AUKUS Pillar II, creating a trilateral framework to share testing facilities and pool technical expertise for both offensive hypersonic systems and counter-hypersonic defenses.
AUKUS Pillar II: The Strategic Context
HACM's development is embedded within the larger AUKUS Pillar II advanced capabilities framework, which encompasses eight technology workstreams including hypersonics and counter-hypersonics, artificial intelligence and autonomy, quantum technologies, and advanced cyber capabilities. In April 2022 the White House announced the AUKUS partners would work together to accelerate hypersonic development specifically under this framework.
Congressional Research Service analysis notes that AUKUS Pillar II appropriations for FY2025 included $69.8 million specifically for work relating to AI, maritime hypersonic tracking and targeting, and air-launched hypersonic cruise missiles — an almost certain reference to HACM-related activity. Legislation passed as part of the 2026 National Defense Authorization Act included the AUKUS Improvement Act to streamline technology sharing, though analysts have noted that the State Department's ITAR exemption failed to narrow the Excluded Technology List as broadly as industry expected, creating continued friction in technology transfer for high-end capabilities such as hypersonics and unmanned systems.
The strategic rationale for urgency is not abstract. China reportedly has five hypersonic missile series in testing or operational use, and has conducted hypersonic tests at a pace U.S. officials have described as vastly exceeding American test frequency. Russia has claimed operational deployment of the Kinzhal air-launched ballistic missile and is developing additional hypersonic systems. The United States is developing three hypersonic weapons programs simultaneously: the Air Force's HACM, the Navy's Conventional Prompt Strike (CPS) system for Zumwalt-class destroyers and Virginia-class submarines, and the Army's Long-Range Hypersonic Weapon (Dark Eagle). CPS achieved successful end-to-end tests in June and December 2024 and again in April 2025 after early test failures, though its deployment to Zumwalt-class destroyers has also slipped from FY2025 to 2027.
The Road to FY2027
The Air Force's current plan, as of this writing, calls for HACM to achieve initial operational capability in FY2027 under the rapid fielding phase of its Middle-Tier Acquisition program. The 13 prototype rounds funded under the rapid prototyping effort serve as test assets, spares, and a residual operational capability. A subsequent major capability acquisition pathway program would begin production in FY2029, informed by the data gathered during the prototype campaign.
To prepare for that transition, the FY2026 budget includes funding specifically for Manufacturing Capacity Enhancements to ensure the industrial base can handle a ramp to full-rate production. The Air Force has revised its transition strategy to prioritize delivering more missiles sooner, improving manufacturability of the design, and expanding production capacity — changes driven by Secretary Meink's explicit directive that any U.S. hypersonic arsenal must be scalable well beyond token quantities.
The presence of an MDA telemetry aircraft over Woomera this week, if it confirms an initial flight test, would mark a milestone long in coming for a program that has faced more scrutiny than its classified profile might suggest. Whether the test — if it occurred — was a propulsion demonstration, a full all-up round flight, or an instrumentation calibration sortie remains unknown. What is clear is that the bilateral machinery underpinning America's most operationally flexible hypersonic weapon is in motion, and the test range for doing so sits not in Nevada or New Mexico, but in the red desert of South Australia.
For a weapon that has traversed fifteen years of scramjet research, survived the cancellation of its predecessor, and absorbed the institutional turbulence of two billion dollars in development spending, the next five flight tests may be among the most consequential in the history of U.S. precision strike.
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