The Pentagon’s plans for future nuclear weapons delivery systems are coming sharply into focus with this year’s budget request. In all the coverage of the exorbitant $1.5 trillion defense top-line, analysts have so far overlooked an important development: clear signs that the next generation of U.S. nuclear weapons delivery systems will be non-ballistic hypersonic missiles and reentry vehicles.
It’s not just the Pentagon’s budget justification documents that provide evidence for this plan. The Department of Energy’s National Nuclear Security Administration (NNSA) has also indicated that it is examining next-generation reentry capabilities that may be hypersonic. Numerous signs point to a coordinated focus across the weapons complex on hypersonic solutions to defeating potential adversaries’ future missile defense capabilities.
Maneuverable, low-flying hypersonic boost-glide weapons and very-high-speed scramjet cruise missiles raise challenges for existing missile defenses. For this reason, Russia has already fielded a hypersonic strategic delivery system: the Avangard hypersonic glide vehicle that is integrated with old SS-19 siloed intercontinental ballistic missiles (ICBMs), although only about a dozen of these are active. Two other Russian hypersonic theater-range weapons, the sea-launched Tsirkon scramjet missile and the air-launched Kinzhal ballistic missile, are nuclear-capable. Since these hypersonic weapons were unveiled in 2018, Russian President Vladimir Putin has repeatedly asserted that concerns about U.S. missile defense were a primary motivation for their development.
Now that the United States is also pursuing hypersonic weapons to improve warhead penetration, several key policy questions arise, including:
- The perennial cost consideration: is a new generation of expensive new delivery systems justified when the current program of record is only just about to crest?
- In a future when U.S. forces are armed with numerous variants of new hypersonic weapons – will strategic stability be strengthened or weakened?
Pieces of the Programmatic Puzzle
One clear indicator of U.S. interest in nuclear boost-glide vehicles exists in the budget justification documents for the twin Navy and Air Force advanced technology development programs on science and technology for nuclear re-entry systems. These two programs will jointly cost about $280 million in fiscal 2027, according to the president’s budget request.
The work funded in these two parallel programs seeks to overcome the technological barriers to future re-entry vehicle designs. The Navy program’s sub-project on future aeroshells notes the need to “withstand extreme temperatures and pressures encountered during hypersonic flight.” The equivalent Air Force justification document explains a recent bump in funding as “increased development and procurement of materials for multiple designs of the high lateral acceleration (high-g) and boost glide [government reference designs].”
Those government reference designs are identified in the Navy materials as the Multi-Service Advanced Capability Hypersonic Test Beds (MACH-TBs), a series of glide vehicles funded by a program directly responsible to the office of the Secretary of Defense. The Navy documents indicate that a warhead fuze sub-project aims to test a prototype fuze in fiscal year 2028 on a MACH-TB vehicle.
The MACH-TB program has been structured around use of the Other Transaction Authority, an alternative to traditional Pentagon contracts that allows for faster agreements with non-traditional contractors and consortiums. So far, the program has awarded two rounds of agreements for test beds that can be integrated with commercial space launch providers as well as conducted several test launches.
Downstream of these early-stage research programs are actual weapons designs. The Air Force this year separated out funding for its next ICBM re-entry vehicle into a new project called Next Generation Reentry Vehicle (NGRV). Although budget documents do not explicitly state that this vehicle will be hypersonic, one hint that it will be is a reference to the NNSA’s WXX warhead program.
According to NNSA budget requests, the agency completed a two-year NGRV technical study – using the same name and acronym – in fiscal year 2023. Then, according to the fiscal 2025 budget request, the program progressed to a two-year concept assessment “on various non‐ballistic reentry vehicles” under the same name, strongly suggesting that next-generation means boost-glide. The fiscal 2026 budget request made clear that the NGRV study is associated with the WXX warhead.
The NNSA’s newly minted Rapid and Advanced Capabilities office is now requesting funding for flight test needs associated with the WXX.
As a reminder, the NNSA and Air Force already are in the early stages of producing a new warhead, the W87-1, and an associated aeroshell, the Mk21A, for the Sentinel ICBM. These programs have separate funding lines from NGRV/WXX and are likely too far advanced to incorporate new technologies that are only now being flight tested. But if we cast back to the NNSA’s fiscal 2024 budget request, the agency notes that NGRV will inform “future aeroshell concepts for the LGM-35A Sentinel,” suggesting that there are – or were – ambitions to create a duplicative set of hypersonic warhead and aeroshell to complement the W87-1/Mk21A combination.
Theater Conjecture
Aside from strategic nuclear weapons, the United States may also be pursuing hypersonic options for its future theater nuclear capabilities as well.
Testifying before the House Armed Services Committee on April 29, Secretary of Defense Pete Hegseth indicated plans are underway.
“Should the department be thinking about a future sea-launched nuclear system with greater survivability, maneuverability, and potential hypersonic capability?” asked Rep. Mark Messmer (R-Ind.), following-up a prior question about the nuclear-capable sea-launched cruise missile.
“Yes, they are,” said Hegseth.
Even if such a program has not yet appeared in budget documents, an early-concept sea-based hypersonic theater nuclear weapon would likely benefit from both the ongoing Navy and NNSA research programs discussed above.
The Air Force has not shown its cards yet, either, but the number of conventional hypersonic programs in Air Force R&D plans that could be adapted for nuclear missions is increasing. This year, the service indicated it hopes to acquire an Air-Launched Ballistic Missile, based on “mature existing hypersonic weapon technologies.” Curiously, the missile is funded as a derivative of the Air-Launched Rapid Response Weapon, a glide vehicle already in production with an estimated 1,600-kilometer range. Both of these co-exist alongside a third weapon, the Hypersonic Attack Cruise Missile, which is based on a scramjet design.
Risks and Implications
The rapid proliferation of U.S. conventional hypersonic weapons programs raises the question of whether acquiring nuclear delivery systems with similar trajectories is advisable.
Speaking before the House Armed Services Committee’s Subcommittee on Strategic Forces in March 2024, a Biden-administration official argued that it wasn’t.
“We are only acquiring conventional hypersonics,” said Michael C. Horowitz, then the deputy assistant secretary of defense for force development and emerging capabilities, because “it’d be a lot less likely that any country including the PRC would view shots of U.S. hypersonic systems as potentially carrying nuclear weapons because we are not developing nuclear-armed hypersonics.”
“Because [Russia and China’s] systems are dual capable that’s why we think they potentially increase the risk of instability,” Horowitz said.
But by March 2024, not only was the NNSA conducting its technical study of next-generation non-ballistic reentry capabilities, the Air Force and Navy were moving in that direction too.
This year’s Air Force budget request reveals that the Mach-TB integration tests are a response to “strategic re-entry environment requirements outlined in the twenty-five (25)-year roadmap jointly developed between the [Air Force and Navy], in accordance with strategic guidance provided by the Office of the Undersecretary of [Defense] for Research and Engineering (R&E) in [fiscal year] 2023.”
In short, the future U.S. nuclear hypersonic weapon is the product of strategic guidance set by the Biden administration’s Pentagon team — although it remains unknown whether the precise requirements derived from that guidance have subsequently been re-interpreted by Trump-administration officials or the services.
Whether or not Horowitz’s statements accurately described the last administration’s concerns about the risks of inadvertent escalation caused by potential mis-characterization of a conventional hypersonic attack, the Trump team clearly does not share them.
Hypersonic nuclear weapons may raise other stability concerns. Because boost-glide weapons can maneuver in flight much more than traditional maneuverable reentry vehicles for ICBMs – although with cost to their speed – their targets may be ambiguous to the defender. This target ambiguity could lead to miscalculation if the defender perceives a strategic attack – or even a decapitating attack – is underway, when it is not.
Hypersonic boost-glide weapons provide a defender much less time to identify the missile on terrestrial missile warning radars, although the problem is not presented to space-based radars. Any country that relies on dual-phenomenology for attack characterization – such as the United States – may face the temptation to abandon that safeguard in the face of hypersonic threats.
On the other hand, if hypersonic weapons improve the penetration of strategic warheads and make strategic missile defenses less effective, strategic stability may benefit overall. But for the United States, which fields the most advanced and sophisticated nuclear arsenal of any nation, the question is whether the cost will be worth it.
The W87-1 warhead and Mk21A aeroshell will cost approximately $30 billion. The Navy’s W93 warhead and its Mk7 aeroshell will cost at least as much. As comparison points, those are likely to be underestimates for a hypersonic delivery system that is a novel endeavor for the United States.
With the bill for other elements of the nuclear modernization program reaching their zenith over the next decade, Washington should consider more cost-effective approaches to improving strategic warhead penetration, such as negotiating restraints on strategic missile defenses with Russia and China. -- Xiaodon Liang, Senior Policy Analyst for Nuclear Weapons Policy and Disarmament