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Analysis//0011/April/2026/London-Dialogue. 27 April 2026
The concept of strategic stability, forged through the long Cold War nuclear standoff, rested on a deceptively simple architecture. It assumed mutual vulnerability between adversaries, an assured second-strike capability on each side, and a temporal cushion long enough for rational deliberation under crisis. Hypersonic weapons, defined by their combination of speeds beyond Mach 5 and atmospheric manoeuvrability, do not merely shift the offence-defence balance within this architecture. They erode the very conditions on which it was constructed. The argument advanced here is that advanced hypersonic systems represent the ultimate challenge to established norms of strategic stability because they collapse the temporal, informational, and epistemic foundations of deterrence. The recent Iran war has, in fragmentary but suggestive form, provided the first operational evidence that this transformation is already underway.
The Conceptual Architecture Under Strain
Strategic stability, as articulated by Thomas Schelling and reframed by contemporary scholars, presumes that adversaries can read each other’s intentions accurately and within a window long enough to choose restraint. Hypersonic weapons compress that window in three distinct ways. First, the trajectory profile of hypersonic glide vehicles (HGVs) and hypersonic cruise missiles (HCMs) flies below the radar horizon, evading early-warning systems originally designed for predictable ballistic arcs. As the Royal United Services Institute has observed in recent commentary, hypersonic systems can fly low enough that terrain itself obscures detection, shrinking the engagement window from minutes to seconds. Second, terminal-phase manoeuvrability defeats the geometric assumptions of interceptor systems, which depend on predictable target trajectories. Third, dual-capable systems generate target ambiguity, since a conventional prompt strike and a nuclear counterforce strike are indistinguishable to sensors during flight.
The cumulative effect, identified in SIPRI’s policy report on hypersonic boost-glide systems, is that both HGVs and HCMs can undermine strategic stability by producing target ambiguity, compressing decision cycles, and eroding the credibility of mutual vulnerability. The RAND Corporation’s study Disrupting Deterrence reaches a complementary conclusion: emerging technologies can undermine deterrence stability by massively enhancing the value of striking first, irrespective of whether either side’s basic deterrent posture remains credible. This is the analytical core of the problem. The challenge is not that hypersonic weapons make deterrence harder, but that they alter the conditions under which deterrent logic operates at all.
The Second-Order Effect
The phrase “deterring deterrence” denotes a second-order effect frequently missed in technology-focused literature. Hypersonic weapons do more than threaten the survival of nuclear forces or command-and-control nodes; they suppress the preconditions on which deterrence rests. If the time available for retaliatory deliberation collapses below the threshold of meaningful human decision, then assured retaliation becomes conditional on automated or pre-delegated launch authority. This is precisely the inversion that Cold War strategists laboured to avoid. Russia’s revised nuclear doctrine of November 2024, which broadened the conditions for nuclear use, illustrates how doctrinal posture is adjusting to a compressed temporal environment, as documented in the SIPRI Yearbook 2025. Independent assessments by the United States Institute of Peace and the Carnegie Endowment for International Peace reach broadly the same conclusion: the threshold for nuclear first use has been lowered, even if the operational implications remain ambiguous.
The Center for Strategic and International Studies has argued that conventional hypersonic strike weapons undermine deterrence by complicating early-warning and increasing the vulnerability of forward-based forces to surprise attack below the nuclear threshold. This subnuclear vulnerability is the analytical heart of “deterring deterrence”. When an adversary can credibly threaten a conventional first strike that disables nuclear command nodes, integrated air defence assets, or sensor architecture, the threshold between conventional and nuclear war becomes porous. The deterrent threshold is itself deterred.
The Iran War as Empirical Inflection Point
The June 2025 Israel-Iran war, and the broader Iranian retaliatory campaigns documented by Al Jazeera, have generated the first sustained operational dataset on hypersonic-class systems in a regional crisis between near-peer adversaries. On 18 June 2025, Iran’s Islamic Revolutionary Guard Corps announced the operational use of the Fattah-1 missile against Israeli targets, claiming penetration of the multilayered Israeli air defence network. The technical reality is more contested. The International Institute for Strategic Studies analyst Fabian Hinz has argued that the Fattah-1 is more accurately characterised as a medium-range ballistic missile with a manoeuvrable re-entry vehicle, possessing only short terminal-phase manoeuvrability rather than full hypersonic glide capability. Researchers from the James Martin Center for Nonproliferation Studies have identified Fattah-1 debris from both the October 2024 and June 2025 strikes.
The strategic significance of the Iran war, however, lies less in the technical fidelity of Iranian claims than in the demonstration effect they produced. Even an imperfect “near-hypersonic” system, fired in salvo against a state with arguably the world’s most sophisticated multi-tier missile defence, generated three observable consequences. First, Israeli interceptor stocks were rapidly drawn down, exposing the asymmetric cost ratio between offensive missiles and defensive interceptors. Second, the political signalling value of hypersonic claims, regardless of technical accuracy, raised the perceived cost of escalation for Israel and the United States. Third, the conflict accelerated the regional diffusion of hypersonic-adjacent technology, vindicating SIPRI’s earlier warning about the gradual diffusion of explicit and tacit missile knowledge and the erosion of Cold War arms control architecture.
This is the transformation implied in the broader thesis. Strategic stability has historically been a P5 problem, governed by bilateral and trilateral nuclear arithmetic. The Iran war suggests that the corrosive effect of hypersonic systems on deterrence is no longer confined to that arithmetic. Regional dyads, with shorter geographic decision cycles, less mature crisis-communication architectures, and weaker doctrinal restraints, will reproduce the instability faster than the great powers ever did.
The Russia-Ukraine and Sino-American Dimensions
The Iran war did not occur in isolation. Russia’s deployment of the Oreshnik intermediate-range missile against Dnipro in November 2024, and again against Lviv in January 2026, alongside its mature Avangard hypersonic glide vehicle programme, has demonstrated the use of hypersonic-class systems for coercive nuclear signalling rather than purely military effect. President Vladimir Putin’s framing of Oreshnik as immune to any missile defence system is, as analysts at the Polish Institute of International Affairs note, technically debatable but strategically consequential. The missile’s purpose is psychological pressure, an exercise in reputational deterrence rather than physical destruction. China’s DF-17, fielded with the DF-ZF glide vehicle, occupies a distinct strategic niche, oriented toward conventional counter-intervention in the Indo-Pacific and the contestation of United States carrier groups.
Across these three theatres, the empirical pattern is consistent. Hypersonic systems are being employed not as decisive battlefield weapons but as instruments for shaping the cognitive environment in which deterrent decisions are made. They generate uncertainty deliberately. The analysis published by the Royal Air Force Centre for Air and Space Power Studiesobserves that hypersonic ambiguity over the offensive or defensive purpose of these systems is itself a destabilising factor, distinct from their physical capabilities.
A Critical Caveat
A rigorous analysis must concede that the erosion-of-stability thesis can be overstated. Three counterarguments deserve weight. First, the arsenals remain small: Russia is believed to possess only a limited number of operational Oreshnik units, and the Avangard regiment at Dombarovsky was scheduled to reach only twelve missiles by 2027. Second, scholars writing in the Texas National Security Review have argued that current procurement decisions in the United States overstate the immediate strategic need for hypersonic weapons and underplay the destabilising signalling effects of acquisition itself. Third, where hypersonic weapons restore mutual vulnerability against advanced missile defence, they may paradoxically reinforce stability rather than erode it, as some Russian strategic analysts argue with respect to Avangard’s role in penetrating US ballistic missile defence.
These caveats matter, but they do not refute the core argument. They qualify the mechanism without altering the direction of travel. The Iran war demonstrated that the destabilising signalling effect of hypersonic claims operates even with technically marginal systems and that the proliferation pathway is open beyond the great powers.
Toward Mutual Predictability
If hypersonic weapons are truly deterring deterrence, the policy implication is that arms control must evolve from a framework of mutual vulnerability toward one of mutual predictability. This requires pre-launch notification regimes for hypersonic tests, declaratory clarity on dual-capable system roles, transparency measures for glide-phase trajectories, and a Missile Technology Control Regime recalibrated to the technical realities of HGVs and HCMs. Without such measures, the conceptual architecture of strategic stability will continue to corrode, not because any single system is decisive, but because the cumulative effect of compressed time, ambiguous intent, and proliferating capability will exceed the cognitive bandwidth of crisis decision-makers.
The Iran war is not yet conclusive evidence of this trajectory. It is, however, the strongest empirical signal to date that the Cold War architecture of restraint is no longer sufficient to govern the strategic environment now emerging. The intellectual task ahead is to construct a successor framework before the next regional crisis, fought with faster and less discriminate systems, demonstrates the cost of intellectual delay.
Dr Tahir Mahmood Azad is Executive Director of London Dialogue, an independent UK-based research and policy institute. He can be reached at [email protected]
Tahir Azad
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