Paint the B-52s Brightly: Reducing Confusion Between Conventional and Nuclear Weapons Is Essential

What if the next war goes nuclear because one side mistakes a conventional missile for a nuclear one, and responds accordingly? This issue of “entanglement,” or the risks of confusing conventional weapons with nuclear ones, and vice versa, deeply concerns us. It is also finally starting to receive the public policy attention it deserves: For example, whether to develop a nuclear variant of the U.S. Tomahawk sea-launched cruise missile has become a relatively important topic in the U.S. Congress. Vice Adm. Johnny R. Wolfe, Jr., the Navy’s director for strategic systems programs, said it best during a defense budget hearing this past May: “Anytime you have a conventional mission with a nuclear mission, you have to be very careful to segregate those and make sure that our warfighters understand how that operates.”

Numerous issues drive the importance of debate on this subject. First, nuclear miscalculation risk is rising, and with it there is an increase in public-facing nuclear policy dialogue. This includes concepts with far-reaching consequences for entanglement and its inherent concerns regarding miscalculation. Second, in the next two years, the world will almost certainly enter an interlude with effectively no nuclear arms control, and ideas for navigating that moment in history include some that could increase entanglement.

Further, indications of how conventional-nuclear entanglement could complicate dynamics in a conflict are now regularly on display. While Russia and China jointly flew nuclear-capable bombers into the Alaska Air Defense Identification Zone in July 2024, the United States used nuclear-capable stealth bombers for conventional anti-ship strikes in exercises in the same month. Some of this is a feature and not a bug — an expected byproduct of the important work of the United States and allied nations in advancing integrated deterrence.

These and other issues mean that entanglement risks should be a major feature of public debates regarding changes to nuclear postures and plans. However, despite some increased attention to the issue in 2024, the debate still does not match the scale of the risks.

To illustrate why the risks of entanglement should be taken more seriously, we begin with a look to the past, as some ideas are emerging today that echo dangerous Cold War dynamics that needlessly complicated conventional planning and operations while driving ambiguity and misinterpretation risks. We also highlight some of the tricks that emerged to mitigate entanglement risks that we can look to for inspiration today, including prosaic solutions such as distinguishing paint marks and physical features to separate conventional from nuclear assets. We then highlight some of the most important conventional-nuclear entanglement issues that are part of today’s security environment or that could evolve in the coming years, before offering some key recommendations for addressing them. The main theme? The U.S. government should avoid conventional-nuclear entanglement as much as possible.

Learning from the Past

Through the early decades of the Cold War, nations pursuing nuclear capabilities often developed nuclear weapon concepts that would leverage conventional weapon designs. This duality was intentional, given material and personnel limitations that the defense community had to manage as Cold War postures emerged.

The Honest John artillery rocket was one of the earliest cases. Over time, it painted a clearer picture of how duality might generate entanglement problems.

Honest John was designed from the start to carry nuclear, chemical, and high-explosive warheads. The Korean War was growing more brutal. As stalemate settled in but its multi-decade future remained unforeseen, U.S. strategists questioned what adding field-deployable nuclear artillery would do to the dynamic on the peninsula. The U.S. Army pursued a crash program of these weapons with this in mind, though the primary use case shifted quickly to the Soviet threat. Honest Johns began moving into Europe in 1954, and by the mid-1960s, the United States had around 2,500 tactical nuclear warheads in Europe for this and other delivery systems. At the time, it was unclear to NATO nations whether the Soviet artillery they saw spreading across Warsaw Pact nations included nuclear variants. As this all evolved, early entanglement lessons emerged.

For nations hosting conventional-only Honest Johns, like Norway and Denmark, their leaders worried that adversaries would estimate that Washington was secretly co-locating nuclear warheads, ready to load at any time. This created major inadvertent-escalation concerns regarding future battles, beyond what would have been the case if all sides were clear on which systems were nuclear-armed. Such potential for confusion limited the utility of the systems for conventional combat. For the nations hosting these weapons, it also became clearer that the personnel time required to handle the deployed nuclear warheads could detract from readiness for conflicts that both sides worried could erupt at any time.

Both sides of the Cold War took unilateral measures to reduce such entanglement. These challenges also informed formal arms control steps. Multiple U.S. treaties with the Soviet Union (later Russia) and their implementation agreements are riddled with good ideas for reducing the odds of one side mistaking the other’s conventional assets for nuclear ones.

The 1991 START I Treaty numerically limited each party’s nuclear warheads and launch systems, and so what would be counted as nuclear vs. conventional became a deeply detailed deliberation. The results enshrined in the treaty and its long annexes instructed that the dual-capable systems covered by the treaty must be distinguishable. The treaty outlined the granularity it would take: “A heavy bomber equipped for long-range nuclear ALCMs [air-launched cruise missiles], a heavy bomber equipped for nuclear armaments other than long-range nuclear air-launched cruise missiles, a heavy bomber equipped for non-nuclear armaments, a training heavy bomber, and a former heavy bomber shall be distinguishable from one another.” Similar categorizations extended to inter-continental ballistic missiles and other treaty-covered items.

With these tasks in hand, the nations’ experts worked to determine how they could best signal and prove to one another that the treaties were being respected. We’re now left with reams of documents with ideas for mitigating entanglement risks, and these ideas should be resurrected.

A 1998 memorandum of understanding for implementing START I includes momentous examples. It describes externally observable distinguishing features for the U.S. B-52G bombers: If one was “equipped for nuclear armaments other than long-range nuclear ALCMs [it] does not have wing strakelets” and it “has no horizontally mounted antennas on the side of the aft fuselage, as compared to the B-52H.” A B-1 bomber in the same category “has no large vertical blade antenna on top of the fuselage near the mid-wing.” The nations also reduced the geographical spread of certain nuclear assets, such as inter-continental ballistic missiles.

The Intermediate-Range Nuclear Forces Treaty included indicators that could be observed by national technical means and through inspections on the ground. Its implementation agreements allowed only certain military transport aircraft to be used for inspections and required that they have “standard markings and paint schemes, to include camouflage.” The call signs to be used for the aircraft would follow a specific formula. Inspectors would wear civilian clothes and special badges to show clearly who they were.

Each side was concerned that the other would keep producing new weapons to replace the ones that they eliminated, and further ideas were developed to handle that challenge. Soviet facilities could continue producing missile launchers — but not for the treaty-banned SS-20 missiles — so long as they had a different number of axles.

In many cases, size differences were viewed as decent indicators of whether items fell under treaty limits, for both weapon items and vehicles used to transport them. At continuous-monitoring sites, “all railcars whose length is less than 14.00 meters and all road vehicles with a cargo section whose length is less than 14.00 meters” could pass through the site gates unimpeded. Each side shared data, diagrams, and photographs to help drive greater clarity on what weapons held which capabilities.

The operational challenges that entanglement brought about, and these subsequent efforts to reduce the blurring of conventional-nuclear lines, have shown that some of the dangers of deliberate duality can be avoided or mitigated going forward.

Looking to the Future

Russia has remained the most static part of this landscape, having maintained more conventional-nuclear entanglement than others for its perceived benefits of ambiguity, including to offset weaknesses relative to NATO in its conventional forces. Several contemporary Russian systems are particularly unclear, including both land- and air-based systems.

A prominent example is the Iskander system, which can launch short-range ballistic and cruise missiles. In 2023, Russia reportedly deployed nuclear-capable Iskander systems to Belarus. The specific capabilities of these deployments remain uncertain but are the subject of intense scrutiny.

Delivery of some newer Russian cruise missiles presents another example of entanglement. In 2015, Russian strategic bombers carried Kh-10 conventionally equipped air-launched cruise missiles to strike targets in Syria. Notably, their bombers are also equipped to deliver nuclear versions of the same cruise missiles. Ground-launched cruise missiles may pose entanglement issues as well. A 2024 U.S. State Department report notes that “Russia has admitted it has developed and fielded nuclear-capable versions of its ground-launched cruise missiles.” The muddled Russian development and deployment of conventional and nuclear systems present serious entanglement risks.

China, for its part, deliberately sidestepped much of this challenge during the Cold War, though concerns are rising that it could follow a path more similar to Russia’s in the near term. A 2023 Department of Defense report to Congress warns that China “may be exploring development of conventionally-armed intercontinental range missile systems,” which if deployed could threaten conventional strikes against the continental United States. The report further concludes that these systems would “present significant risks to strategic stability.” Even without specific conventional inter-continental ballistic missile systems, China has co-located nuclear and conventional missile systems in the past, complicating the management of a potential conflict. If China pursues development and deployment of conventionally armed inter-continental ballistic missiles, encouraging China to devise ways to signal conventional- versus nuclear-armed systems will be important.

The DF-26 intermediate range ballistic missile system is the only notable current Chinese weapons system presenting clear conventional-nuclear entanglement with both nuclear and conventional missions. China first fielded the DF-26 in 2016 and continues to expand this system and, as the 2023 Defense Department report notes, “the multi-role DF-26 is designed to rapidly swap conventional and nuclear warheads and is capable of conducting precision land-attack and anti-ship strikes in the Western Pacific, the Indian Ocean, and the [South China Sea] from mainland China.” The specifics of nuclear versus conventional DF-26 deployments remain opaque, but some analysts have assessed that the warheads are swappable between nuclear and conventional based on the launcher design. Available indicators thus far, including at least one notable exercise where the People’s Liberation Army Rocket Force switched between conventional and nuclear missions during the exercise, suggest the missile is truly dual-capable, which amounts to a significant entanglement issue during wartime.

As the first nuclear-armed nation, the United States led the field in realizing potential entanglement issues. The country moved forward with a mix of single- and dual-capable systems for decades, but in the latter decades of the Cold War, it made significant progress in reducing entanglement issues. Such steps included both formal agreements with the Soviet Union and unilateral decisions, such as the Presidential Nuclear Initiatives of the 1990s simply canceling some of the remaining dual-capable, tactical nuclear weapons such as the nuclear-armed Tomahawk missile.

Still, multiple assets with conventional and nuclear missions remain or have long been in development, and in some cases, for important reasons. These include F-15E and F-16C dual-capable aircraft, and the stealthy F-35A that was certified to carry B61-12 nuclear gravity bombs in March 2024.

These capabilities reflect a relative steady state in the U.S. approach to dual-capable systems, and so today, the more important question for the United States is whether and how it will seek to mitigate entanglement risks in its future plans and posture — and in how it manages the balance in existing assets. In current deterrence policy debates, no weapon embodies this pivot point more than the lingering question over whether to develop and reintroduce a new nuclear sea-launched cruise missile to the U.S. Navy.

The Presidential Nuclear Initiatives started the process of pulling nuclear Tomahawk sea-launched cruise missiles out of service, and their retirement was concluded in 2013. Over that time, the Navy has continued to expand the range of capabilities that conventional Tomahawks have, and the Army also chose to modify Tomahawk into ground-launched cruise missiles after the Intermediate-Range Nuclear Forces Treaty ended. Tomahawks are heavily relied upon — according to their manufacturer, they’ve been used “in an operational environment more than 2,350 times” — to the point that a Navy overview describes them as “the weapon of choice for the U.S. Department of Defense.” These weapons have also become a key feature of U.S. efforts to enhance defenses and deterrence alongside allies. In addition to the United Kingdom being a longtime host, conventional Tomahawk sales are now extending to Japan and the Netherlands, and to Australia as part of the AUKUS agreement.

These factors alone give a sense of how adding a dual nuclear capability could get complicated and possibly quite dangerous. Yet the Trump administration’s Nuclear Posture Review initiated plans to do just that. The subsequent Biden administration’s posture update killed that plan, though Congress has been resurrecting it with funding and a requirement that the Department of Defense make it a program of record.

In addition to the miscalculation risks that this could entail, as highlighted by Wolfe’s testimony quoted above, it is crucial to ask whether a nuclear Tomahawk variant would affect operations of these important conventional weapons. Indeed, in the same hearing, Sen. Mark Kelly raised the specter of nuclear sea-launched cruise missiles hindering our conventional missile capacities and other operations during a conflict. “One of my biggest concerns,” he stated, “is that we would be giving up something we really need for something we are unlikely to use.”

The issues extend beyond the weapons systems. For more than a decade, defense leaders and experts have weighed how overlap in conventional and nuclear systems related to command, control, communications, and warning raises or lowers the bar for both conventional and nuclear conflict, and how it might benefit or detract from deterrence. The misinterpretation risks abound, as do concerns that solely conventional systems could be more likely to be targeted in ways that drive escalation in conflict. The Department of Defense has made acquisition and programmatic moves toward disaggregating such systems in recent years, yet the entanglement question will remain as their modernization continues in the years ahead. Steps by Russia and China to break down space-related norms will surely shape how this unfolds.

Recommendations

Recognizing the geopolitical challenges involved with any nuclear steps taken by possessing countries, there are multiple reasons for minimizing conventional-nuclear entanglement — and mitigating its risks where it persists — even if solely for self-interest. Chief among them should be that no nation is served by being targeted with a nuclear strike from an opponent’s miscalculation regarding a non-nuclear attack they conduct. In short, nobody benefits from accidentally triggering a nuclear strike on themselves. It follows that there’s no upside to making your conventional attack look like a nuclear one.

There are strategic deterrence and operational benefits as well. Clarity that an asset is nuclear can sharpen signaling. More and more, nations and alliances are betting that they can manage escalation, including de-escalation, after an adversary crosses the nuclear threshold. This is untested, to be sure, but regardless, entanglement problems would make such de-escalation less predictable for everyone, given how prepped a battlefield would be for each side to misread each other in the fog of a conflict gone nuclear. And given that nuclear nations may seek arms control agreements or mutual restraint in the future, this should shape their planning as well. Future agreements are likely to take place in an environment of relatively low trust, and reduced entanglement with conventional assets can lead to simpler, less intrusive nuclear verification options.

The U.S. government should avoid conventional-nuclear entanglement as much as possible. Beyond sea-launched Tomahawks, conventional systems like ground-launched cruise missiles should simply remain conventional. Remaining conventional-only is especially important for the highly capable Joint Air to Surface Standoff Missiles and their extended-range variants, which feature a growing list of allied possessors including Australia, Finland, Poland, Japan, and Germany.

The issue should also be part of integrated deterrence dialogues and planning with allies, in particular given that those with geographic proximity to Russia, North Korea, and China are left even more vulnerable to potentially devastating fallout from miscalculations. Of course, all nuclear-armed nations should be encouraged to follow suit, even if this is not tied to formal negotiations or processes.

In the near term, all relevant nations should prioritize measures to reduce miscalculation risks in cases where entanglement is likely to persist or grow. The U.S. and Chinese governments raised missile launch notifications in nascent nuclear talks, and should maintain this focus if discussions carry forward. Other forms of warning and communication could be better than their absence, even if no one can be fully confident that any side will believe another.

In many cases, the United States has been showing a responsible balance of showcasing conventional-nuclear integration with transparency and predictability. A nuclear-capable stealth bomber took out a surface ship with a conventional guided bomb for the first time this summer when the B-2 Spirit bomber joined the annual Rim of the Pacific exercise. The capability signaling was certainly strong, yet it was clearly an exercise, and publicly (and likely privately) communicated. Likewise, the U.S. government has shown sensitivity to timing ballistic missile test launches to mitigate the risks of misinterpretation by Russia during its war in Ukraine.

A looming decision for the United States will be whether to convert some number of conventional B-52H Stratofortress bombers to the nuclear mission if the New START Treaty expires in early 2026 without a replacement teed up. If this occurs, the United States should maintain the treaty’s standard that nuclear and non-nuclear bombers remain distinguishable, whether visibly or through maintaining separate basing locations. Unlike with more modern stealth aircraft, this is a case for which the Air Force’s much-loved attractive paint jobs could come in handy.

Conclusion

Even if nations stick with muted tones and tasteful patterns, clear and distinguishable features like paint markings are just one of many possible options that can be adapted from history or newly developed as nations work to mitigate conventional-nuclear entanglement risks in what could be perilous years ahead. Many options are relatively easy to do, and many can be done unilaterally to reduce the risk of catastrophes, even in the absence of formal political or legal commitments.

It is worth noting explicitly that we are confident that planners and strategists across the U.S. government are developing and employing these sorts of options on a continual basis. Yet all nations should plan their reactions for navigating the odds that Russia will maintain its long-held approach of leveraging conventional-nuclear ambiguity and possibly increase this dangerous behavior as it updates its nuclear use doctrine, and that China may seek to follow suit. In the face of this challenge, it will be tempting to mimic Vladimir Putin’s actions, yet this only raises risks for the United States and its allies. As the earliest initiator of conventional-nuclear entanglement, the United States has also been out front in managing and mitigating risks involved with this phenomenon for decades — a leadership role that it is more important than ever to maintain.

Christine Parthemore is the chief executive officer of the Council on Strategic Risks and former senior advisor in the Office of the Assistant Secretary of Defense for Nuclear, Chemical, and Biological Defense Programs. Her work covers issues in countering weapons of mass destruction, arms control and disarmament, biosecurity and biodefense, innovation and technology trends in national security, and the security implications of a broad range of global risks.

Catherine Dill is director of operations at the Council on Strategic Risks and was previously senior research associate at the James Martin Center for Nonproliferation Studies. Her research portfolio covered nuclear and missile developments in East Asia, sanctions evasion and illicit trafficking networks, and developments in strategic trade control systems.

Image: Senior Airman Tiffany Emery

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