In March 2025, a joint Army and Navy test team launched a hypersonic missile from a Pacific range facility and watched its glide body streak through the upper atmosphere at more than five times the speed of sound, maneuvering as it flew. The Pentagon confirmed afterward that the weapon hit its target and validated its speed, range, maneuverability, and what officials called its “survivability” against defenses. Nine months earlier, a separate test had already proven the full end-to-end performance of the closely related Conventional Prompt Strike missile. Two successful flights in under a year marked a turning point: the United States now has boost-glide weapons that work, and no country on Earth has publicly demonstrated a reliable way to shoot them down.
That asymmetry between offense and defense is what makes hypersonic glide vehicles, or HGVs, the most destabilizing class of weapons to emerge since the cruise missile. Military planners in Washington, Tokyo, and across NATO are grappling with a threat they can track only partially and intercept not at all. Understanding why requires looking at what these weapons actually do in flight, what the United States has proven it can build, and how far the defensive response still has to go.
Why the glide phase changes everything
A conventional ballistic warhead follows a path that missile defense systems were built to exploit. It rises on a booster, coasts through space along a predictable parabolic arc, and falls toward its target. Radars can detect the launch, compute the trajectory within minutes, and cue an interceptor to meet the warhead in midcourse or during its terminal descent. Decades of U.S. missile defense investment, from Ground-based Midcourse Defense to the Aegis SM-3 family, rest on that predictability.
An HGV breaks the model. After separating from its booster at high altitude, the glide body does not coast through space. Instead, it dives back into the upper atmosphere and rides the boundary between space and air, sometimes skipping off the denser layers below like a stone across water. At speeds above Mach 5, it can execute lateral maneuvers, shift its aim point, and vary its altitude in ways that make its future position far harder to calculate. A detailed Congressional Research Service report on U.S. hypersonic weapons development explains the core problem: midcourse interceptors are designed to hit objects on ballistic trajectories in space, and HGVs spend most of their flight doing something entirely different. The glide phase happens at altitudes too low for space-based interceptors and too high and fast for most surface-to-air systems, creating a defensive gap that no fielded weapon currently fills.
What the United States has proven on offense
After several years of mixed results, including embarrassing ARRW flight test failures in 2021 and 2022 that stalled the Air Force’s air-launched program, the Pentagon’s boost-glide portfolio has turned a corner.
The first breakthrough came in June 2024, when the Department of Defense completed what it described as an end-to-end flight test of the all-up-round hypersonic missile associated with the Navy’s Conventional Prompt Strike and the Army’s Long-Range Hypersonic Weapon programs. A Pentagon press release stated the test “validated end-to-end performance data,” meaning the booster, the Common Hypersonic Glide Body (C-HGB), the guidance system, and all supporting components functioned together from launch through impact. That language is significant. Earlier tests had evaluated subsystems in isolation. This was the first publicly confirmed flight of the complete operational weapon.
The March 2025 joint Army-Navy test went further. Pentagon officials said the flight confirmed the missile’s speed, range, maneuverability, altitude profile, and survivability against defenses. That last word matters. “Survivability” implies the test scenario modeled or simulated a defended environment and that the glide body performed as designed under those conditions. While the specifics remain classified, the public characterization signals confidence that the weapon can penetrate at least some categories of existing air and missile defense.
Together, these two tests establish that U.S. hypersonic boost-glide technology has moved from developmental stumbles into repeatable, full-scale flight demonstrations. The CRS report catalogs the broader portfolio: the Army’s LRHW battery, the Navy’s CPS for integration on Virginia-class submarines and Zumwalt destroyers, the Air Force’s HACM (Hypersonic Attack Cruise Missile), and several DARPA-managed technology feeders including the Tactical Boost Glide program. Not all of these are at the same readiness level, but the glide body at the center of CPS and LRHW now has real flight data behind it.
The competition Washington does not discuss openly
The United States is not developing these weapons in a vacuum. Russia declared its Avangard HGV operationally deployed in December 2019, mounted atop modified SS-19 ICBMs. Independent verification of Avangard’s performance is limited, and Western analysts have questioned how many units Russia has actually fielded, but the system’s existence is not in dispute. More consequentially for the Pacific, China has conducted flight tests of the DF-ZF glide vehicle since at least 2014 and is believed to have fielded it on DF-17 medium-range ballistic missiles. The Department of Defense’s annual China Military Power Report has tracked these developments for years, and the DF-27, a longer-range system reportedly capable of reaching Guam and beyond, has appeared in U.S. intelligence assessments as an emerging capability.
This competitive landscape is the unstated backdrop to nearly every U.S. hypersonic investment decision. The Army did not accelerate LRHW because boost-glide physics are elegant. It did so because potential adversaries fielded the technology first, and the Pentagon concluded it needed both a matching offensive capability and a way to defend against incoming glide vehicles. That defensive piece is where the hardest unsolved problems remain.
Building a shield that does not yet exist
The U.S. Missile Defense Agency and Japan’s Ministry of Defense have signed a cooperative development agreement to build the Glide Phase Interceptor, or GPI. The program targets exactly the defensive gap described above: the atmospheric glide segment where HGVs maneuver and where no current interceptor has a proven kill capability.
GPI is designed to integrate with the Aegis combat system, the ship-based radar and missile network already deployed on U.S. and allied destroyers and cruisers worldwide. If the program succeeds, GPI would ride existing Aegis launchers and leverage existing sensor networks rather than requiring an entirely new platform. That integration approach is pragmatic, but it also introduces constraints. Aegis ships carry a finite number of missile cells, and every GPI round loaded displaces a Standard Missile or Tomahawk. Force planners will eventually face hard tradeoffs about how many interceptors they can afford to carry.
As of mid-2025, GPI has not produced a test intercept. The engineering challenges are severe. The interceptor must survive closing speeds that could exceed Mach 10 combined, maintain aerodynamic control in the thin upper atmosphere, and receive accurate targeting updates against an object that is actively maneuvering. Budget documents suggest the Missile Defense Agency is targeting initial fielding in the late 2020s, but past missile defense timelines have slipped repeatedly, and no public MDA statement commits to a firm date for initial operational capability.
The U.S.-Japan partnership itself carries strategic weight beyond the hardware. Allied co-development of a hypersonic defense interceptor signals that both governments view the glide-phase threat as serious enough to share sensitive technology and integrate it into shared naval platforms. That institutional commitment is a form of evidence about threat perception, even before the interceptor proves it can hit anything.
What the public record cannot tell you
Significant gaps remain in what outside analysts can assess. No publicly available U.S. government source provides detailed data on the exact skip trajectories HGVs follow, the plasma sheath effects that may blind tracking sensors during high-speed glide, or the failure rates of tests that did not succeed. The Pentagon’s press releases describe successes; they do not catalog the engineering problems encountered along the way.
Cost is another black box. Neither the Pentagon nor Congress has released reliable per-unit cost estimates for operational hypersonic weapons. These systems require exotic thermal protection materials, precision manufacturing, and specialized boosters, all of which suggest high unit costs. If each round costs tens of millions of dollars, the calculus of when and how to use them changes dramatically. The same uncertainty applies to GPI: no authoritative public estimate exists for what each interceptor will cost or how many a realistic production run could deliver.
DARPA’s role as a technology incubator adds another layer of opacity. The CRS report references DARPA programs alongside service-specific weapons, but declassified technical results from efforts like Tactical Boost Glide have not been released. Budget justifications confirm the programs exist and receive funding. They do not reveal how much of the current hypersonic portfolio rests on proven physics versus still-maturing materials and guidance technologies.
Reading the evidence without the hype
The strongest evidence available comes from two categories: official Pentagon press releases confirming specific test events, and the CRS report that synthesizes program details from budget documents and congressional testimony. These are primary sources with named institutional authors and clear accountability. When the Department of Defense states that a test “validated end-to-end performance data,” that language is carefully chosen and reviewable. It confirms the system worked as designed in a controlled test. It does not confirm battlefield effectiveness against an actual adversary’s layered defenses.
Readers should also parse the Pentagon’s own characterizations carefully. The assertion that HGVs provide “survivability against defenses” reflects the design intent of the weapon and the conditions of a specific test, not an independent assessment of whether any real adversary’s defenses have been tested against it. The CRS judgment that HGV glide behavior “challenges existing missile defenses” describes a theoretical vulnerability grounded in physics, not a documented combat outcome. Until a hypersonic glide vehicle is used against a modern, layered defense in actual conflict, its true effectiveness will remain partly a matter of informed estimation.
Where the offense-defense race stands in 2025
The scoreboard, as of June 2025, is lopsided. On offense, the United States has flown its boost-glide weapons successfully in back-to-back tests and confirmed their core performance characteristics. China and Russia appear to have fielded their own HGV systems even earlier. On defense, no country has publicly demonstrated a reliable ability to intercept a maneuvering glide vehicle in its atmospheric flight phase. GPI is the most serious attempt to close that gap, but it remains years from a proven intercept, let alone operational deployment.
That imbalance has consequences beyond the laboratory. If offensive hypersonic weapons work as advertised and defensive systems lag behind, the strategic assumptions underpinning missile defense in the Western Pacific and in Europe shift. Carrier strike groups, forward bases, and allied territory that once sat behind Aegis and THAAD umbrellas may be more exposed than planners assumed a decade ago. The weapons that skip through the upper atmosphere at Mach 5 and above have not yet been used in war, but they have already changed the calculations of the people preparing for one.
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*This article was researched with the help of AI, with human editors creating the final content.
