The advanced missile was originally scheduled for its first flight test in 2024, but developers RTX and Northrop Grumman have confronted mounting delays over its advanced propulsion system.

The US Air Force’s long-awaited Hypersonic Attack Cruise Missile (HACM) has finally entered flight testing—and as the test venue highlights, it is not the only nation waiting!

The Air Force has confirmed that the first test of the HACM had taken place not in the United States, but in a test range in Australia. The US Air Force and Royal Australian Air Force are co-producing the HACM, and have divided responsibility for its creation, which has run significantly behind schedule.

“The US Air Force, in partnership with Australia, has conducted a flight test of the Hypersonic Attack Cruise Missile (HACM) as part of our continuous work to advance long-range strike capabilities,” an Air Force spokesman announced this week, according to The War Zone. “Leveraging this enduring alliance, the Royal Australian Air Force executed the release of a HACM flight test unit over a designated Australian test range, gathering crucial data to advance the program’s objectives.”

It remains unclear when and where the test actually took place, and whether the HACM flew under its own power or merely glided after its “release” from an aircraft. Still, these questions aside, the test represents a significant milestone for a weapon that was originally scheduled to begin flight testing two years ago, in 2024. The question now is how quickly the Air Force can accelerate the delayed program from testing to operational service.

What Is the HACM Missile?

The AHM-4 HACM (pronounced “hack-em”), awarded to prime contractor RTX (Raytheon) by the US Air Force in 2022, is an air-launched, air-breathing hypersonic weapon. Developed by RTX and Northrop Grumman, the program draws technology from DARPA’s Hypersonic Air-breathing Weapon Concept (HAWC) and the US-Australia SCIFiRE hypersonic research partnership. The initial operational launch platform is expected to be the F-15E Strike Eagle, though it will likely be added to other aircraft over time—particularly as Australia, a full partner in the project, does not fly the F-15E.

The HACM is fundamentally different from boost-glide hypersonic weapons. According to the GAO, the missile consists of two stages: a rocket booster and a scramjet-powered cruise vehicle. In the first stage, the booster accelerates the weapon to extreme speeds; though the missile’s precise speed is still unconfirmed, all “hypersonic” weapons operate at speeds of Mach 5 (3,800 mph) or above. In the second stage, the scramjet takes over for sustained hypersonic flight, and the cruise vehicle eventually dives toward the target.

The scramjet component is important. While conventional jet engines use rotating compressors to compress incoming air, a scramjet exploits an aircraft’s tremendous forward velocity to compress air entering the engine. Combustion can therefore take place even while the airflow remains supersonic, which jet engines have trouble with at extreme speed. The advantages here are sustained hypersonic speed, maneuverability, and a smaller form factor than some boost-glide weapons. Of course, scramjets do pose difficult engineering problems of their own; operations at Mach 5-plus are inherently difficult and maintenance-heavy—a notion that HACM’s delays reinforce.

Australia Has Been an Invaluable Partner on HACM Development

The partnership between the US and Australia on HACM has been unusually collaborative, building on more than 15 years of joint hypersonic research.

In the recent test, the RAAF conducted the release and collected data under realistic flight conditions. The test site wasn’t disclosed, but the most likely location is the enormous Woomera Test Range in sparsely-inhabited South Australia. Woomera is ideal for such a test, as it provides an enormous and remote testing area, limited population, and room for extended high-speed flights—all with relative secrecy.

Now the program needs to accelerate. The original flight test target was 2024; the fact that it took until late 2026 highlights the problems the program has had in its development. The GAO has warned that the HACM had “zero margin” remaining in its schedule, and that the Air Force has now “taken on risk” to maintain the schedule. As the obvious theater for the HACM’s use will be the Indo-Pacific, and the People’s Liberation Army Navy (PLAN) continues the buildup of its armed forces, time is of the essence.

About the Author: Harrison Kass

Harrison Kass is a writer and attorney focused on national security, technology, and political culture. His work has appeared in Tablet, City Journal, The Hill, The Spectator, and The Cipher Brief. He holds a JD from the University of Oregon and a master’s in Global & Joint Program Studies from NYU. More at harrisonkass.com.

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