Dual-use distinguishability: How 3D-printing shapes the security dilemma for nuclear programs

ABSTRACT

Additive manufacturing is being adopted by nuclear programmes to improve production capabilities, yet its impact on strategic stability remains unclear. This article uses the security dilemma to assess incentives for arms racing as the emerging technology becomes integrated into nuclear supply chains. Innovations sow the ground for competition by making it easier to produce weapons and harder to distinguish civil from military motives. But additive manufacturing could still mature into an asset by revealing greater information about nuclear aspirants. Beyond the nuclear realm, the article refines offense-defence theory to explain how changes in non-military technology shape the practice of deception.

KEYWORDS:

• Nuclear proliferation
• emerging technology
• additive manufacturing
• arms races
• security dilemma

Over the last five years, political leaders and technical experts alike heralded additive manufacturing – more commonly known as digital 3D-printing – as an emerging technology with ‘the potential to revolutionise the way we make almost everything’, including military hardware.¹ Analysts quickly identified the technology as ‘a prospective game changer’ with ‘significant national security implications’ because it utilised breakthroughs in robotics, computation and network connectivity to fabricate components with unprecedented levels of complexity from digital blueprints.² In 2013, for instance, a team from the Center for New American Security claimed, ‘additive manufacturing could fundamentally impact the defense industrial base … by dramatically increasing the pace of moving from prototype to production and by enhancing the flexibility and adaptability of production lines.’³ Other scholars underscored the possibility for 3D-printing to ‘enable the rapid integration of new technologies whenever a design breakthrough occurs’,⁴ especially if it offered the ability ‘to make (almost) anything, anywhere’.⁵

These forecasts proved prescient as aerospace and defence firms leveraged additive manufacturing to make sophisticated components for jet engines, missiles and satellites, often at a fraction of the cost and time of traditional production processes.⁶ To no surprise, nuclear weapons enterprises also began to invest in the technology to reap similar benefits.⁷ At the same time, key players in the civil nuclear industry – from General Electric Hitachi to Rosatom and the Chinese National Nuclear Corporation – adopted additive manufacturing for peaceful purposes because it could ‘potentially reshape the very nature of supply chains’.⁸ Research and development efforts focused on 3D-printing nuclear reactor components with ‘new complex designs’, including nuclear fuel rods and large pressure vessel cylinders.⁹ As a result, the technology started to improve and expand upon the traditional menu of options for manufacturing nuclear capabilities.

Unfortunately, defence experts still struggle to explain how the looming adoption of additive manufacturing by nuclear programmes will affect strategic stability.¹⁰ On initial consideration, it seems like this novel means of production might sow the ground for arms race instability and even interstate conflict by enabling the next wave of clandestine proliferation. As the National Nuclear Security Administration reported in 2017, future improvements in additive manufacturing could ‘create new and worrisome pathways to nuclear weapons’, while an early report from the National Defense University highlighted the risk of the technology ‘being used to render detection of nuclear proliferation more difficult’.¹¹ The Defense Science Board went so far as to speculate that the technology might enable nonnuclear weapon states to march towards the bomb with greater secrecy, speed, and ease than before. As the study concluded, the diffusion of ‘such a capability could create game-changing technological surprise and potential vulnerability’, thereby pressuring nations to consider preventive measures at the earliest sign of proliferation.¹²

Yet additive manufacturing is merely the latest manifestation of an emerging technology with the potential to change the likelihood of competition and conflict over nuclear programmes. As Bernard Brodie cautioned during the Cold War,

what may look like extraordinarily important changes in the tools of war or in related technologies may appear to lack significant impact on strategy and politics … even though those improvements may look quite significant to a scientist or to an engineer.¹³

To be sure, a few innovations in nuclear technology set the foundation for periods of heightened tension, such as the consideration and employment of military force against gas centrifuge plants or heavy water reactors. But many other breakthroughs in production technologies of similar lineage to additive manufacturing, notably the maturation of automated precision machine tools, ended up having little observable impact on interstate relations in this context. Moreover, some changes in the technology available to states – for example, the spread of light water reactors or remote sensing methods – lowered the risk of conflict and dampened arms race incentives by providing options for nuclear energy-aspirants to reveal motives and verify peaceful commitments.

Given this mixed track record, I refine a theory of interstate competition – the security dilemma – to determine how emerging technology impacts strategic stability among nations with nuclear programmes. This framework provides a solid foundation to explore when it is difficult for nations to reveal benign motives while accumulating technology that is dual use in nature, meaning it has ‘both peaceful and military applications’.¹⁴ In a twist on the offense-defence variables at the heart of the security dilemma, I show that emerging technology can change the material capacity to produce atomic weapons and the information environment for distinguishing motives. My theory claims that innovations in the global pool of nuclear technology shape the security dilemma by making it easier or harder to distinguish military from energy aspirants. I use this logic of dual-use distinguishability to shed light on the consequences of additive manufacturing if it becomes further integrated into nuclear supply chains. On the one hand, additive manufacturing could create periods of intense competition making investments in energy infrastructure indistinguishable from weapons programmes. But the digital nature of additive platforms could also make patterns of peaceful nuclear behaviour more transparent, thereby enabling energy aspirants to better distinguish themselves and escape from the security dilemma altogether.

Beyond the nuclear realm, the theory presented in this article contributes to scholarship on the role of technology and information in world politics. By reformulating the classic concept of offense-defence distinguishability to better account for how changes in the dual use nature of technology enable states to practice disinformation, my framework helps us understand the structural sources of deception among nations.¹⁵ I find that new technologies set the stage for competition when they make civilian investments indistinguishable from military enterprises. But in line with the central theme of this special issue, I also identify the conditions under which technologies stabilise arms race incentives by enabling states to reveal non-military motives with relative ease.¹⁶ As such, my core concept of dual-use distinguishability complements the expansion of the offense-defence balance by Ben Garfinkel and Allan Dafoe to account for levels of technology investment.¹⁷ In addition, as Heather Williams points out, the general notion of arms control is predicated on the ability to make clear distinctions between weapon platforms.¹⁸ I show how distinguishability becomes even more critical when dealing with the underlying latent capacity to produce military forces. Indeed, governments are struggling to grapple with the challenges presented by the availability of dual-use technologies today, from computer networks and artificial intelligence to autonomous systems and unmanned aerial vehicles.¹⁹ As new innovations push states onto the horns of the old dual-use dilemma, this article identifies clear incentives for states to develop technologies in ways that reveal the motives of various aspirants.

On the policy front, my analysis highlights the need to track and guide how additive manufacturing and other new technologies impact the distinguishability of nuclear programmes in the years ahead. The problem is that it will be difficult to manage the impact of additive manufacturing in this manner, as no single nation or industrial entity controls this global pool of technology. Whereas major innovations ‘used to be “born secret” and remain controlled from cradle to grave’ by individual governments, the rise of multinational industry as the stewards of global science and technology means that new technologies are now ‘essentially ungoverned’.²⁰ In the nuclear domain, however, states can leverage cartels such as the Nuclear Supplier Group (NSG) and international institutions to manage the structural impact of emerging technologies. As a result, the article recommends closer collaboration among industry leaders, national governments and international institutions to ensure additive manufacturing matures into an asset rather than a liability for nuclear energy programmes.

The article is organised into five parts. The first offers a primer on the novel features of additive manufacturing for nuclear proliferation and identifies analytic gaps in the literature. The second section refines the security dilemma to better account for variation in the nature of nuclear production technology. The third section derives hypotheses about how additive manufacturing changes the likelihood of arms racing and conflict. The fourth section crafts indicators to guide future empirical research into additive manufacturing and dual-use distinguishability. The final section concludes with implications for the study and practice of non-proliferation.

Additive manufacturing and nuclear proliferation

What is additive manufacturing and how might this emerging technology change the future of nuclear proliferation? This section reviews the technical features of the new production platform to identify how it promises to improve upon the existing pool of technologies used by nuclear programmes. Nuclear weapon states and civil nuclear suppliers are adopting the technology because it offers a more versatile and cost-effective way to fabricate components with complex designs that could not be made before with traditional methods. The concern is that these same benefits could turn into proliferation liabilities if the technology expands nuclear production options while blurring the distinction between peaceful and military applications.

Additive manufacturing refers to a family of production technologies with two unique features.²¹ The first is the additive process of fabrication, whereby an object is built by laying down successive layers of material. This new principle stands in contrast to subtractive methods of manufacturing that use various cutting tools – such as lathes, mills and grinders – to remove material from a larger object. By building objects from scratch, additive manufacturing provides the ability to make components with complex geometries and special characteristics simply not possible before with subtractive machine tools. Many of the top aerospace, defence and nuclear firms are therefore adopting additive manufacturing to expand the available menu of production options.

Second, additive manufacturing represents a leap forward in automation and supply chain optimisation because it leverages robotics, computation and network connectivity to fabricate components from digital build files. These blueprints contain the all of the design information needed to produce a final component, as well as the commands and specifications that guide the automated fabrication process itself.²² This type of cyber-physical manufacturing builds upon the previous generation of computer numeric controlled (CNC) subtractive machine tools, which still require skilled machinists with deep experience to operate. The ultimate goal of additive manufacturing is to capture this tacit knowledge in the digital realm, where it can be automated, saved and even transmitted to distant locations, thereby enabling parts to be printed on demand wherever needed. As a result, the digital nature of the technology promises to shrink down or even eliminate global logistics and supply chains.

The taproot of the proliferation problem is that additive manufacturing is already being adopted by nuclear programmes to reap similar benefits. The nuclear laboratory complex in the United States is pioneering the adoption of AM because it believes the technology ‘could have broad impact across [nuclear] weapons components and materials.’²³ Other nuclear weapons enterprises may be investing in the technology as well.²⁴ On the civil nuclear energy side of the coin, enterprises in the United States, South Korea, Russia and China are exploring ways to integrate the technology into production lines. Early efforts are underway to fabricate the critical components at the heart of a nuclear reactor, from methods for 3D-printing nuclear fuel at Idaho National Lab to large metallic pressure vessels by the Chinese National Nuclear Corporation.²⁵

Additive manufacturing offers these nuclear programmes an agile and efficient means of production, especially amid supply chain atrophy in the United States and Europe.²⁶ Small batches of reactor components, for instance, can be difficult and expensive to source if they are produced using traditional methods, as producers often need long lead times to establish processes for forging and casting parts.²⁷ In stark contrast, additive manufacturing plants can be quickly repurposed to fabricate parts without retooling production lines or interpreting designs.²⁸ The ultimate goal is to leverage the digital nature of the technology to print nuclear certified parts, thereby reducing quality control concerns.²⁹ If additive manufacturing technology continues to mature along its current trajectory, it could help lower the massive costs associated with new nuclear reactor projects or stockpile stewardship by providing a steady-state capacity to produce a wide range of certified nuclear components on demand.

The concern is that these same features of additive manufacturing could enhance clandestine proliferation while making it difficult to verify the peaceful nature of nuclear energy programmes. For nuclear weapons-aspirants, this new production technology holds the promise of maturing in ways that (1) lower the barriers to entry, (2) accelerate and augment traditional development pathways, and (3) subvert detection and export controls. First, additive manufacturing could ‘significantly reduce the expert knowledge required to produce dual-use parts, as an increasing amount can be coded into digital build files.’³⁰ One non-proliferation assessment concluded that, ‘the only true barriers to operationalizing 3D printing for the manufacture of illicit items involve obtaining the 3D printers themselves, the materials used in 3D printing, and the sensitive [digital build files].’³¹ Theft or transfer of these digital files could spread far more information about sensitive nuclear components than traditional blueprints. Second, additive manufacturing could shrink down development timelines or expand options for the production and weaponisation of fissile material. One of the main benefits of the technology is that it ‘promises to reduce lead times due to its ability to rapidly produce prototypes, facilitating testing and design processes.’³² Nuclear programmes could therefore accelerate the lengthy process of building up tacit knowledge and mastering production processes.

Third, additive manufacturing could erode architectures for monitoring and regulating nuclear technology.³³ In facilities equipped with additive manufacturing, for instance, ‘it is less obvious what is actually being built in comparison to a factory with subtractive tools, where casting molds or special tools are being used.’³⁴ The digital nature of 3D-printing is even more worrisome, as it offers the ‘potential to produce any physical object based on technical data in the form of build files. These can be easily transferred using email or other means of electronic communication that are hard for authorities to detect and prevent.’³⁵ Additive manufacturing could therefore ‘subvert traditional nodes of trade in the physical commodity supply chain or alter the ways that dual-use technology, knowledge, and skills are transferred around the world.’³⁶ If illicit procurement networks exploit the technology to hide more deception points among commercial activities, it may become difficult to identify peaceful patterns of nuclear trade. Such a breakdown in export controls and intelligence ‘could both allow an undesirable transfer to take place and prevent the collection of information that could be used for verification purposes.’³⁷ As a result, the integration of digital 3D-printing into above-board supply chains could erode confidence in peaceful commitments by nuclear energy programmes.

Yet it remains unclear how these future proliferation risks will impact interstate relations.³⁸ As noted at the outset of this article, defence analysts offer a wide-range of predictions, from a future where nations live in fear of surprise proliferation to scenarios that resemble the status quo. But none draw upon a theory of conflict or specify the mechanisms that link additive manufacturing to competition among nations. Of course, there is a robust literature on military action against nuclear programmes.³⁹ However, this work often overlooks how changes in the pool of technology available to states might exacerbate or dampen the incentives to strike. Other scholars refine bargaining models to explore the impact of technology diffusion,⁴⁰ uncertainty⁴¹ and investments in military capabilities⁴² on the likelihood of preventive war, but they treat nuclear technology in pure military terms as the means to acquire nuclear weapons. The other articles in this special issue tackle a complementary set of issues by specifying how investments in emerging technologies impact the offense-defence balance,⁴³ arms control⁴⁴ and conflict initiation,⁴⁵ but these careful contributions largely focus on innovations beyond the traditional arena of nuclear proliferation.

We therefore lack a theory that addresses how changes in the dual-use nature of nuclear technology for both weapons and energy programmes can shape the parameters for arms racing and war. To fill this gap, I lay down a theory of the conditions under which technological innovations impact the likelihood of conflict based on a refinement to the well-known model of interstate crises – the security dilemma.

Emerging technology and proliferation security dilemmas

In this section, I refine a venerable theory of interstate crises – the security dilemma – to explain how technological change in the process of proliferation affects the likelihood of conflict. First, I review the security dilemma literature to identify the impact of military technology on the propensity for competition among nations. I narrow this logic to explain why the security dilemma exhibits variation across different types of nuclear programmes that all draw from the same global pool of technology. Second, I specify how new technologies can impact this security dilemma by enhancing the capacity to produce nuclear weapons and the ability to distinguish military from civilian motives.

Nuclear investments and the security dilemma

The security dilemma explains when investments in military or economic capabilities intended to make oneself more secure end up having the opposite effect by triggering competition and conflict with other nations.⁴⁶ The crux of the problem is that the accumulation of power ends up challenging the security of other states, who respond by balancing against or even using force to mitigate the perceived threat of aggression. The dilemma arises when nations cannot forego power to assuage the fears of rivals, lest they become vulnerable to predation in the anarchic realm of world politics. However, ‘the security dilemma can vary across time and space’ because some material investments avoid triggering intense arms race spirals.⁴⁷ Under some conditions, nations can dampen the risks of conflict while building up power.

What factors drive variation in the security dilemma? According to one strand of international relations theory, the nature of military technology establishes parameters on ‘how many and what kind of arms’ should be procured for protection without engendering negative blowback.⁴⁸ The security dilemma tends to be mild when (1) it is easier and cheaper to invest in defensive capabilities, and (2) other states can clearly distinguish between different types of military postures.⁴⁹ But these material and informational factors can change as new technologies emerge. When weapons that ‘protect the state also provide the capability for attack, and other states cannot differentiate between offensive and defense stances,’ the security dilemma becomes severe.⁵⁰ Since states struggle to send and receive accurate information in this world, worst-case assumptions must be made about motives, thereby creating conditions ripe for competition and conflict. As a result, the security dilemma depends on the impact and distinguishability of military technology available to states at any given point.

How does nuclear technology shape these parameters of the security dilemma? In terms of material impact, an investment in nuclear infrastructure and knowledge increases a country’s level of nuclear latency: its capacity to manufacture atomic weapons on short notice.⁵¹ Unlike other forms of military technology, nuclear-aspirants can build up latent capabilities over long periods of time while remaining confident that the ‘culmination of their investment, a nuclear weapon, will not become obsolete.’⁵² Once a nuclear programme can produce the fissile material at the core of the bomb with enrichment and/or reprocessing (ENR) facilities, it can convert nuclear latency into military force with a high degree of efficiency. As a technical measure of bomb-making capability, latency is agnostic on the distinction between peaceful and military motives.⁵³ The challenge from an informational perspective is that energy and weapons programmes both draw from the same pool of nuclear technology, so it can be difficult to distinguish civilian from military investments. This dual-use nature of nuclear technology means that latent capabilities developed by civilian energy programmes can also ‘be used to overcome scientific challenges associated with the production of nuclear weapons.’⁵⁴ As a result, the accumulation of latency – even for peaceful energy purposes – sets the stage for the security dilemma by threatening others with the prospect of proliferation.

When a country appears to be in pursuit of nuclear weapons, an intense security dilemma is likely to emerge that leaves the purported proliferator with less security for three reasons. First, proliferation often threatens another rival, ‘which then has to initiate its own nuclear weapons program to maintain its national security.’⁵⁵ The net result from these ‘chains of proliferation’ is that the nuclear aspirant ends up ‘less secure in the proliferated region than if the region had no such weapons.’⁵⁶ Second, preventive motivations for war become acute because proliferation represents a looming shift ‘in bargaining power – specifically, deterrence capability – that cause actors to fear being disadvantaged in the future.’⁵⁷ Rivals face strong pressures to forestall this adverse shift in the balance of power. Third, the pursuit of nuclear weapons creates a closing window of opportunity for rivals to attain the most favourable position with military force before it becomes incredible to threaten the nuclear-armed defender. Taken together, these instability mechanisms link the process of proliferation to the heightened risk of conflict under a severe security dilemma.

Upon deeper examination, however, the security dilemma exhibits variation across a range of nuclear programmes that invest in similar technologies. Some proliferators delay or dampen the most pernicious effects of the instability mechanisms by emulating peaceful motives and practicing deception. Other energy-oriented programmes invest in fuel enrichment plants and plutonium reprocessing facilities but escape from the security dilemma altogether. How do these countries invest in dual-use nuclear technology while avoiding the security dilemma? The solution is to signal peaceful motives and implement non-proliferation commitments that are ‘relatively immune to future geopolitical or domestic change.’⁵⁸ In practice, the nuclear-aspirant can (1) limit the capacity to produce nuclear weapons and accept an intrusive monitoring regime to verify compliance; (2) give up the nuclear programme itself as a type of hostage by accepting enhanced vulnerability to preventive action or dependence on foreign suppliers⁵⁹ ; and (3) bring in third parties to underwrite non-proliferation commitments.⁶⁰ In essence, these assurance mechanisms provide a menu of options for nations to stabilise the risks of conflict while investing in nuclear technology.

The impact of emerging technology

The instability and assurance mechanisms help to specify how technological innovations can change two central parameters at the heart of the proliferation security dilemma: (1) the material capacity to produce nuclear weapons and (2) the informational ability to differentiate military from civilian motives. The first dimension examines how the technology changes the process of proliferation. Given the deep pool of technologies available, does the innovation enable nations to produce and/or weaponise fissile material with relatively greater ease, speed or secrecy than before? To be sure, ‘technologies often do not live up to their promise’, and not all innovations alter longstanding proliferation pathways.⁶¹ Some emerging technologies can actually make it harder for less-developed nations to make progress, given the high absorption capacity requirements of advanced technology.⁶² For an emerging technology to affect the security dilemma, it must have a positive change in how nations go about developing nuclear latency, otherwise it drops out of the analysis. This establishes a necessary condition to scope down the universe of emerging technologies to those with the potential to augment the threat of proliferation.

As Figure 1 demonstrates, variation in the security dilemma therefore depends on the second dimension of dual-use differentiation: does the emerging technology make it easier or harder for nations to distinguish military from civilian motives with high confidence? Some innovations reveal more accurate information about the future trajectory of nuclear programmes by tapping into ‘dimensions and characteristics that will influence or predict … later behavior’, and cannot be manipulated to practice deception.⁶³ When an innovation shapes the pool of nuclear technology in this manner, the decision to invest in nuclear assets conveys ‘inherent evidence’ about how the nation ‘will behave under various circumstances’.⁶⁴ In this improved informational environment, nuclear energy programmes can more readily use technology to send credible signals of peaceful motives, thereby dampening the security dilemma. At the same time, weapons-aspirants will find themselves exposed and unable to emulate these peaceful patterns of nuclear behaviour.

Figure 1. Material and informational effects of emerging technology.

Technological innovations can also make it harder to differentiate motives in the nuclear arena. In one extreme world, there is no meaningful distinction between military and civilian investments in nuclear technology. To be sure, this condition only existed at the dawn of the atomic age when ‘no civilian uses of the new technology existed’ until the first nuclear energy revolution in the 1950s.⁶⁵ The pure military nature of nuclear technology at the time made it impossible for political leaders or even fellow scientists to reassure each other, so ‘the world saw a situation of fears and preemptive motives emerging no matter what one did.’⁶⁶ Since technical steps towards the bomb could not be distinguished from the peaceful pursuit of nuclear energy, any investment in nuclear capabilities threatened other nations and ratcheted up the prospect of conflict.

But emerging technology need not push us back into this situation to exacerbate the security dilemma. By simply making it harder to distinguish motives, new innovations can muddy the grey zone between clear civil and military applications of nuclear technology. Indeed, this moderate level of indistinguishability is codified in Article II of the Non-Proliferation Treaty (NPT), which contains the core commitment not to manufacture nuclear weapons without prohibiting specific activities or technologies. This means many dual-use technologies – from uranium enrichment to shaped high explosives and additive manufacturing today – fall squarely in this grey area because they are fungible across civilian and military sectors. When innovations further blur the distinction between prohibited and permitted activities, it becomes harder for energy programmes to allay suspicions, while enabling weapons-aspirants to practice deception. As a result, this type of decrease in dual-use distinguishability tends to pull nuclear programmes into an intense security dilemma.

In sum, emerging technology can increase the risk of competition and conflict over nuclear investments by (1) enhancing the capacity to produce nuclear weapons and (2) decreasing the ability to distinguish civilian from military motives. Figure 1 above shows how emerging technology shapes these core material and information variables of the security dilemma. To recap, the first dimension stipulates that an innovation must make it easier to develop nuclear latency. When this necessary condition is satisfied, the second dimension focuses on whether the innovation makes it easier or harder to distinguish civilian from military motives. As Figure 2 demonstrates, the impact of emerging technology on this informational parameter of dual-use distinguishability ends up driving the severity of the security dilemma.

Figure 2. Impact of dual-use distinguishability on the nuclear security dilemma.

The next section uses this theory to derive more specific propositions about the future likelihood of interstate crises as additive manufacturing technology shapes the process of proliferation.

Hypotheses

How could additive manufacturing impact the likelihood of competition and conflict as it becomes integrated into nuclear programmes over the next decade? Drawing upon the refined logic of the security dilemma, this section crafts four main hypotheses about the relationship between additive manufacturing technology and onset of interstate crises over nuclear proliferation.

At the outset, it is crucial to consider the null hypothesis that additive manufacturing does not enhance the material capacity to produce nuclear weapons. Emerging technologies do not always change the political strategies that nations adopt to accumulate and wield power. Even an incredible new means of production such as additive manufacturing may ultimately have no effect on the pathways to the bomb or the credibility of non-proliferation commitments. Moreover, there are sound reasons to be sceptical about the consequences of manufacturing technology on the process of proliferation. Additive platforms may improve the means of producing nuclear components, but this breakthrough need not alter how nations go about developing fissile material facilities or reassuring others of peaceful intent. As Scott Kemp argues, nations have long been able to produce subcritical gas centrifuge components with rudimentary machine shops, so the value added from advanced manufacturing techniques may be negligible.⁶⁷ The null hypothesis should therefore be accepted if the maturation of additive manufacturing fails to usher in demonstrable change in pathways to the bomb, especially relative to the existing menu of production options.

Null Hypothesis – No Difference (H₀): Additive manufacturing does not change the process of building up nuclear latency relative to traditional technologies, so it ends up having no impact on the likelihood of competition.

The null hypothesis can be rejected if and when indicators emerge that additive manufacturing alters the development of nuclear latency. In this world, the intensity of the security dilemma would then come to depend on variation in the level of dual-use distinguishability.

On one extreme end of the distinguishability spectrum (see Figure 2), additive manufacturing could change the nature of nuclear latency by making it impossible to distinguish between investments motivated by the pursuit of nuclear energy or nuclear weapons. Since peaceful motives become difficult to send or receive among nations, any investment in nuclear infrastructure ratchets up the threat of proliferation. The only way to reassure others is to abstain from building nuclear assets. But restraint is dangerous because a rival can present a fait accompli by drawing from the enhanced pool of production technologies to rapidly manufacture nuclear weapons in secret. As a result, ‘there is no escaping the horns of this dilemma: building capability cannot guarantee security, but failing to do so can guarantee insecurity.’⁶⁸ Chain reactions accelerate and preventive war motivations become acute as nations hedge against strategic surprise by developing nuclear capabilities in secret while taking steps to neutralise rival nuclear programmes at the earliest stage of development.⁶⁹ The likelihood of conflict is high in this future because additive manufacturing makes the instability mechanisms worse while eroding the credibility of non-proliferation commitments.

Hypothesis 1 – Indistinguishability (H₁): If additive manufacturing changes the information environment for nuclear latency so that civilian applications cannot be distinguished from weapons-oriented endeavours, then states are likely to spiral into intense security dilemmas with strong incentives for competition and military action.

At the other end of the spectrum, additive manufacturing could enable nations to make clear distinctions between peaceful and military motives in the nuclear realm. Under this condition, energy programmes can escape the security dilemma by revealing accurate information about benign motives while resolving the commitment problem intrinsic to nuclear technology. The key is that weapons-oriented programmes cannot emulate these signals and commitment devices, as the nature of technology makes it too costly or difficult to accomplish military objectives behind a false mask of peaceful intent.⁷⁰ The pursuit of nuclear weapons becomes a dangerous affair for proliferators; technical steps towards the bomb send out a clear signal of military motivations that is difficult for the proliferator to plausibly deny. Other nations should balance against and contain this clear proliferation threat. At the same time, nuclear energy programmes can integrate technology in ways that reveal clear evidence of peaceful use. For example, the digital nature of additive manufacturing could be used to reveal greater information about supply chain activities, thereby allowing others states and the IAEA to verify peaceful declarations. Additive manufacturing would thereby set the technical foundation for energy programmes to dial up nuclear latency without threatening others and increasing the risk of conflict.

Hypothesis 2 – Clear Distinguishability (H₂): If additive manufacturing makes it prohibitively difficult for nuclear weapons aspirants to emulate patterns of peaceful use, then nuclear energy programmes can invest in latent capabilities without sparking competition and conflict.

Finally, additive manufacturing may blur the boundaries of the grey zone between peaceful and military motives in the middle of the distinguishability spectrum. In this case, additive manufacturing would be the latest manifestation of an enduring challenge about how best to separate the wolves from the sheep when emerging technology degrades the accuracy of information about nuclear motives and erodes the credibility of non-proliferation commitments.⁷¹ A proliferator would then be able to leverage this ambiguity to hide underneath an opaque patina that masks the ultimate military motives of its production activities.⁷² By enabling plausible deniability and the practice of deception, additive manufacturing would open up new options for proliferators to dampen or delay the most dangerous machinations of the security dilemma. Of course, nuclear energy programmes could end up in a sticky wicket if it becomes difficult to convince others of nuclear restraint.

Hypothesis 3 – Moderate Distinguishability (H₃): If additive manufacturing further blurs the distinction between peaceful and military motives in the nuclear realm, then weapons and energy programmes are both likely to be pulled into mild security dilemmas, albeit for different reasons.

Taken together, this set of hypotheses provides a map for navigating the future landscape of interstate relations as additive manufacturing becomes adopted by nuclear programmes.

Indicators

From a research design perspective, the primary goal of this paper is to refine theory rather than test hypotheses.⁷³ The paucity of open-source data also makes it difficult to conduct a plausibility probe or employ more systematic methods of theory evaluation. Instead, I use the theory to guide empirical research by establishing indicators of the type of evidence needed for both hypothesis testing and process tracing.⁷⁴

To reject the null hypothesis, we would need to see additive manufacturing being integrated into supply chains in ways that change the process of developing nuclear assets. One indicator to track here is whether 3D-printing offers novel benefits for proliferation beyond just lowering specific production hurdles. Of course, clandestine weapons programmes are by definition difficult to observe, and there is no evidence yet in the open-source that ‘3D printing is definitively in use to develop or aid in the production or delivery of [nuclear weapons].’⁷⁵ Instead, another more observable metric is data from the civil nuclear industry on the value added from additive manufacturing relative to traditional production technologies. As discussed below, the cyber-physical nature of additive manufacturing is driving the migration of tacit knowledge and design information into the digital realm, with the ultimate goal of transforming the supply chain for nuclear technology. To be sure, it is still too early to make a confident measurement, since many of these efforts are still at the research and development stage. But this space should be watched as the technology matures in the years ahead.

If additive manufacturing does start to change the means of nuclear production, what type of evidence would help us determine variation in dual-use distinguishability? First, national intelligence agencies and the IAEA have long been able to distinguish civilian applications of nuclear technology from weapons-oriented endeavours with varying degrees of certainty.⁷⁶ The key indicator here is whether technological change enhances or degrades the accuracy of these estimates. So, an extreme shift towards dual-use indistinguishability is only possible if additive manufacturing prohibits nuclear energy programmes from signalling peaceful motives or credibly committing to restraint. To this end, analysts ought to track whether additive manufacturing enables (1) a significant breakthrough in the efficiency of uranium enrichment or (2) a major reduction in the amount of fissile material needed for core of a nuclear explosive device. By lowering the technical requirements for producing and then manufacturing fissile material into an atomic weapon, these changes could make peaceful investments difficult to distinguish from military programmes with high confidence.

Second, as additive manufacturing is integrated into supply chains, we should closely watch for signs of nuclear activities becoming more difficult to monitor, regulate and safeguard. One worrisome indicator would be malicious use of the technology by nuclear weapons-aspirants to steal digital build files, subvert export controls and practice deception by exploiting dual-use ambiguity to deny military objectives. In particular, the relative indistinguishability of additive manufacturing could enable proliferators to build production lines in plain sight rather than sequester them away at suspicious facilities. Nuclear energy programmes would face a vexing challenge when it comes to signalling peaceful intent in this uncertain information environment. If additive manufacturing allows weapons-aspirants to emulate the behaviour of energy programmes, countries may need to go to greater lengths to reassure others and dampen the security dilemma. To illustrate what this may look like in concrete terms, consider a scenario where an advanced civil nuclear programme develops a new additive manufacturing method to print enriched uranium fuel elements for nuclear reactors on demand. During a routine safeguard check of the company’s facilities, including physical production lines and its computer database of digital design information, ‘an inspector discovers a digital build file for printing a spherical object out of plutonium. The company claims the design is part of an experimental project not intended for weapons production. Would this activity clearly violate the country’s obligation to forego the manufacture of nuclear weapons?’⁷⁷ At a minimum, this type of moderate indistinguishability would arouse suspicion about the motives of nuclear energy programmes.

Third, additive manufacturing could lay the technical foundation to further clarify patterns of peaceful nuclear use. While the digital nature of the technology may present a liability, we should track whether the ability to collect and analyse large amounts of data from manufacturing systems could create an opportunity to gain enhanced information visibility into supply chain activities. As one recent assessment pointed out, ‘suppliers of manufacturing equipment and services, including metallic 3D printer systems, have already built remote monitoring sensors into these platforms to collect large amounts of data for business purposes.’⁷⁸ If this digital network morphed into ‘an interconnected web of devices and machines comprising aboveboard supply chains for nuclear capabilities,’ such an Internet of Nuclear Things could ‘provide a novel way for suppliers to maintain continuous custody over sensitive information, machines, and material, and enhance their ability to verify the end-use and end-user of sensitive capabilities.’⁷⁹ As a result, it behoves analysts to determine whether investments intended to reap commercial dividends – such as collecting vast amount of nuclear manufacturing data – could be flipped into an ‘invaluable resource on legitimate procurement and production patterns, making it easier to discern clear signatures of peaceful use.’⁸⁰ In such an environment, nuclear weapons-aspirants and illicit procurement networks would find it challenging to exploit additive manufacturing without setting off clear alarm bells.

Implications for research and policy

In this paper, I refine the security dilemma to better account for the relationship between technological change and interstate competition over nuclear programmes. This theory provides a useful foundation because it specifies how the accumulation of power can result in dangerous arms race spirals, especially when the nature of technology makes it easier to field offensive forces and difficult to distinguish defensive postures. In the context of nuclear proliferation, I show how emerging technology shapes the parameters at the core of security dilemma by changing the material capacity to produce atomic weapons and the information environment for sending accurate signals about peaceful motives. I use this logic to derive hypotheses about the impact of additive manufacturing on the likelihood of competition and conflict over nuclear programmes. If additive manufacturing makes it harder to differentiate military from civilian motives with high confidence, then nuclear investments are likely to beget arms races and conflict. On the other hand, if additive manufacturing improves the ability of nuclear energy programmes to reveal peaceful motives, then weapons-aspirants will find it difficult to practice deception by hiding among the sheep. In this ideal world, countries could reap the benefits of integrating additive platforms into civil nuclear supply chains while dampening the security dilemma at the same time.

The logic of dual-use distinguishability contributes to a recent wave of international relations scholarship at the intersection of nuclear strategy and proliferation. Although scholars have long recognised the potential for nations to exploit the dual-use nature of nuclear energy technology, most theories of proliferation operate from the assumption that the level of distinguishability remained constant throughout the atomic era.⁸¹ Given the scope of technological progress over the last seventy-five years, however, it is reasonable to explore whether we can observe variation in dual-use distinguishability over time. In addition, groups of states have banded together into cartels (e.g., the NSG) and institutions (e.g., the IAEA) in part to shape the pool of options available to nuclear aspirants.⁸² By changing the nature of proliferation threats and assurances, such shifts in the information environment could help to explain patterns in the strategies and tactics of proliferation, as well as the use of nuclear latency to deter aggression and compel concessions in world politics.⁸³

When it comes to the future of non-proliferation policy, the theory underscores that additive manufacturing may not have much impact on the process of proliferation until it matures into a viable production capability. Traditional supply-side remedies such as export controls may be premature unless the specific technical risks come into focus. But additive manufacturing need not spark a major proliferation crisis for it to have a destabilising effect on international relations. If the technology further blurs the distinction between peaceful and military motives, then a number of nuclear energy programmes will find it increasingly difficult to allay suspicions. States face incentives to forestall such an outcome by working to ensure that additive manufacturing helps to reveal aspirant motives as it becomes adopted by nuclear programmes around the world.

Indeed, there is an opportunity at this early stage of technological diffusion to turn additive manufacturing into an asset rather than a liability for nonproliferation.⁸⁴ The industrial pioneers of additive manufacturing in the civil nuclear sector may be willing to work proactively with governments and the IAEA to better protect intellectual property while securing the integrity of sensitive supply chain operations against malicious intrusion. If suppliers and recipients of nuclear technology use digital production capabilities embedded within a larger Internet of Nuclear Things architecture, then the technology could reveal more information about the trajectory of nuclear investments than safeguards and non-proliferation promises do at present. Nuclear energy programmes would face strong economic and security reasons to join this system, thereby leaving weapons-aspirants on the outside exposed to espionage and sabotage.

Acknowledgements

For exceptional feedback, the author is grateful to Andrew Reddie, Ariel Petrovics, Wyatt Hoffman, Brian Rose, Grant Christopher, Ulrich Kühn, Neil Narang, Jane Vaynman, numerous government officials and industry representatives, as well as participants in workshops hosted by the Carnegie Endowment for International Peace in Washington, the Center for Global Security Research at Lawrence Livermore National Laboratory, the Nuclear Policy Working Group at UC Berkeley, the ISODARCO Winter Course in Andalo, the Stanley Foundation in conjunction with the Leibniz-Gemeinshaft in Berlin, and especially the Project on Strategic Stability Evaluation (POSSE). This research was funded in part by the MacArthur Foundation and the CWMD Systems Office within the Office of the Assistant Secretary of Defense for Nuclear, Chemical, and Biological Defense Programs. Bert Thompson provided superb research assistance at Carnegie.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was supported by the John D. and Catherine T. MacArthur Foundation; the CWMD Systems Office in the Office of the Assistant Secretary of Defensefor Nuclear, Chemical, and Biological Defense Programs; and the Carnegie Corporation of New York through seed funds from the Project on Strategic Stability Evaluation (POSSE).

Notes on contributors

Tristan A. Volpe

Tristan A. Volpe is an Assistant Professor in the Defense Analysis Department at the U.S. Naval Postgraduate School. He is also Non-resident Fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace. The views in this article are the author’s own and do not reflect those of the Department of Defense or the US government.

Notes

¹ Barack Obama, State of the Union Address, 12 February 2013, The American Presidency Project.

² Connor McNulty, Neyla Arnas, and Thomas Campbell, ‘Toward the Printed World: Additive Manufacturing and Implications for National Security’ Defense Horizons, 73 (2012) 1–16. For similar forecasts, see Thomas Campbell et al., ‘Could 3D Printing Change the World? Technologies, Potential, and Implications of Additive Manufacturing’ Strategic Foresight Report (Washington, DC: Atlantic Council, October 2011); T.X. Hammes, ‘3-D Printing Will Disrupt the World in Ways We Can Barely Imagine’ War on the Rocks, 28 December 2015; Tate Nurkin, ‘Disruptive Impact: Technological Revolutions Raise Nuclear Risks’ IHS Jane’s Intelligence Review (May 2016) 30–34.

³ Shawn Brimley, Ben FitzGerald, and Kelley Sayler, ‘Disruptive Technology and U.S. Defense Strategy’ (Washington, DC: Center for New American Security, September 2013) 14.

⁴ Michael C. Horowitz, ‘Coming Next in Military Tech’ Bulletin of the Atomic Scientists, 70/1 (2014) 59.

⁵ Neil Gershenfeld, ‘How to Make Almost Anything: The Digital Fabrication Revolution’ Foreign Affairs, 91/1 (2012) 46.

⁶ For an overview, see Trevor Johnston, Troy D. Smith, and J. Luke Irwin, ‘Additive Manufacturing in 2040’ (Santa Monica, CA: RAND Corporation, 2018).

⁷ See e.g. U.S. Department of Energy, National Nuclear Security Administration, Fiscal Year 2016 Stockpile Stewardship and Management Plan, Report to Congress (March 2015) 3–13; U.S. Department of Energy, National Nuclear Security Administration, ‘Labs in NNSA lead the way in 3D printing – the next industrial revolution’ Press Release, 13 June 2016.

⁸ Ian Stewart, Dominic Williams, and Nick Gillard, ‘Examining Intangible Technology Controls – Part 2: Case Studies’ (London, UK: King’s College London, June 2016) 18. Office of Nuclear Energy, ‘Neet-Advanced Methods for Manufacturing Award Summaries’ US Department of Energy, May 2016; Press Release, ‘GE Hitachi Selected to Lead U.S. Department of Energy Advanced Nuclear Technology Research Project’ General Electric, June 2016; Clare Scott, ‘ROSATOM Announces New Additive Manufacturing Subsidiary’ 3DPrint.com, 13 February 2018.

⁹ Zeses Karoutas, ‘3D Printing of Components and Coating Applications at Westinghouse’ MIT Workshop on New Cross-cutting Technologies for Nuclear Power Plants (NPPs), 30 January 2017.

¹⁰ In line with the special issue, this article defines strategic stability in terms of (1) arms race incentives in peacetime and (2) conflict initiation during a crisis, see Todd S. Sechser, Neil Narang, and Caitlin Talmadge, ‘Emerging Technologies and Strategic Stability in Peacetime, Crisis, and War’, Journal of Strategic Studies (2019), 727–735.

¹¹ ‘Prevent, Counter, and Respond – A Strategic Plan to Reduce Global Nuclear Threats’ Report to Congress (Washington, DC: National Nuclear Security Administration, November 2017) sec. 1.7; McNulty, Arnas, and Campbell, ‘Toward the Printed World: Additive Manufacturing and Implications for National Security’, 3.

¹² ‘Technology and Innovation Enablers for Superiority in 2030’ Defense Science Board Report (Washington, DC: Department of Defense, October 2013) xx, 67.

¹³ Bernard Brodie, ‘Technological Change, Strategic Doctrine, and Political Outcomes’ in Historical Dimensions of National Security Problems ed. Klaus Knorr (University Press of Kansas, 1976), 263.

¹⁴ Matthew Fuhrmann, Atomic Assistance: How Atoms for Peace Programs Cause Nuclear Insecurity (Cornell University Press, 2012), 2.

¹⁵ On the production and exploitation of deception, see Austin Carson, Secret Wars: Covert Conflict in International Politics (Princeton University Press, 2018); Erik Gartzke and Jon R. Lindsay, ‘Weaving Tangled Webs: Offense, Defense, and Deception in Cyberspace’ Security Studies 24/2 (2015) 316–48.

¹⁶ Sechser, Narang, and Talmadge, ‘Emerging Technologies and Strategic Stability’.

¹⁷ Ben Garfinkel and Allan Dafoe, ‘How Does the Offense-Defense Balance Scale?’ Journal of Strategic Studies (2019), 736–763.

¹⁸ Heather Williams, ‘Asymmetric Arms Control and Strategic Stability: Scenarios for Limiting Hypersonic Glide Vehicles’ Journal of Strategic Studies (2019), 789–813.

¹⁹ In this special issue, see Jacquelyn Schneider, ‘The Capability/Vulnerability Paradox and Military Revolutions’ Journal of Strategic Studies (2019), 841–863; Michael C. Horowitz, ‘When Speed Kills: Autonomous Weapon Systems, Deterrence, and Stability’, Journal of Strategic Studies (2019), 764–788. See also Jürgen Altmann and Frank Sauer, ‘Autonomous Weapon Systems and Strategic Stability’ Survival 59/5 (2017) 117–42; Heather M. Roff, ‘The Frame Problem: The AI “Arms Race” Isn’t One,’ Bulletin of the Atomic Scientists 75/3 (2019) 95–98; Natasha E. Bajema, ‘Countering WMD in the Digital Age: Breaking Down Bureaucratic Silos in a Brave New World’ War on the Rocks, 13 May 2019; Ulrich Kühn, ‘Can We Still Regulate Emerging Technologies?’ Carnegie Endowment for International Peace, 9 May 2019, https://carnegieendowment.org/2019/05/09/can-we-still-regulate-emerging-technologies-pub-79125.

²⁰ Zachary S. Davis, ‘Ghosts in the Machine: Defense against Strategic Latency,’ in Strategic Latency and World Power (Lawrence Livermore National Laboratory, 2014): 22.

²¹ Brett P. Conner et al., ‘Making Sense of 3-D Printing: Creating a Map of Additive Manufacturing Products and Services’ Additive Manufacturing, 1/4 (2014) 64–76.

²² Logan D. Sturm et al., ‘Cyber-Physical Vulnerabilities in Additive Manufacturing Systems: A Case Study Attack on the .STL File with Human Subjects’ Journal of Manufacturing Systems 44/1 (2017) 154–64.

²³ U.S. Department of Energy, National Nuclear Security Administration, Fiscal Year 2016 Stockpile Stewardship and Management Plan, Report to Congress (March 2015) 3–13.

²⁴ It is difficult to move beyond speculation based on the small number of press releases and public announcements about AM investments issued by nuclear programmes in countries such as Russia, China, India, Pakistan, and North Korea. For an excellent estimate of North Korea’s AM capabilities, see the annex by Joshua Pollack in Robert Shaw et al., ‘Evaluating WMD Proliferation Risks at the Nexus of 3D Printing and Do-It-Yourself (DIY) Communities’ (Monterey, CA: James Martin Center for Nonproliferation Studies, October 2017).

²⁵ ‘Idaho National Lab’s “AMAFT” Makes 3-D Printed Nuclear Fuel That Reduces Risk of Meltdown’ 3Ders, 21 September 2017.

²⁶ Wyatt Hoffman and Tristan A. Volpe, ‘An Internet of Nuclear Things: Emerging Technology and the Future of Supply Chain Security’ Policy Analysis Brief, The Stanley Foundation, June 2018, https://www.stanleyfoundation.org/publications/pab/IoNTPAB618.pdf.

²⁷ Supply chain delays and quality control issues have plagued major civil nuclear companies in the United States and South Korea, see Choe Sang-Hun, ‘Scandal in South Korea Over Nuclear Revelations’ The New York Times, 3 August 2013; Diane Cardwell and Jonathan Soble, ‘Westinghouse Files for Bankruptcy, in Blow to Nuclear Power’ The New York Times, 29 March 2017.

²⁸ Rianne E. Laureijs et al., ‘Metal Additive Manufacturing: Cost Competitive Beyond Low Volumes’ Journal of Manufacturing Science and Engineering 139/8 (2017) 081010–081010–19.

²⁹ W. E. King et al., ‘Laser Powder Bed Fusion Additive Manufacturing of Metals; Physics, Computational, and Materials Challenges’ Applied Physics Reviews 2/4 (2015) 041304.

³⁰ Kolja Brockmann and Sibylle Bauer, ‘3D Printing and Missile Technology Controls’ (Stockholm, Sweden: SIPRI, November 2017) 3.

³¹ Shaw et al., ‘Evaluating WMD Proliferation Risks’, 8.

³² Brockmann and Bauer, ‘3D Printing and Missile Technology Controls’, 6.

³³ Grant Christopher, ‘3D Printing: A Challenge to Nuclear Export Controls’ Strategic Trade Review, 1/1 (2015) 18–25; Matthew Kroenig and Tristan Volpe, ‘3-D Printing the Bomb? The Nuclear Nonproliferation Challenge’ The Washington Quarterly 38/3 (2015) 7–19.

³⁴ Marco Fey, ‘3-D Printing and International Security: Risks and Challenges of an Emerging Technology’ (Peace Research Institute Frankfurt Report, 2017) 28.

³⁵ Kolja Brockmann and Robert Kelley, ‘The Challenge of Emerging Technologies to Non-Proliferation Efforts: Controlling Additive Manufacturing and Intangible Transfers of Technology’ (SIPRI, 2018) 2.

³⁶ Wyatt Hoffman and Tristan A. Volpe, ‘Internet of Nuclear Things: Managing the Proliferation Risks of 3-D Printing Technology’ Bulletin of the Atomic Scientists 74/2 (2018) 104.

³⁷ Stewart, Williams, and Gillard, ‘Examining Intangible Technology Controls – Part 2: Case Studies’ 1.

³⁸ For an assessment on how these trends might shape the menu of non-proliferation options available to the United States, see Tristan A. Volpe, ‘Atomic Inducements: The Case for “Buying out” Nuclear Latency’ The Nonproliferation Review 23/3–4 (2016) 481–93.

³⁹ Rachel Elizabeth Whitlark, ‘Nuclear Beliefs: A Leader-Focused Theory of Counter-Proliferation’ Security Studies 26/4 (2017) 545–74; Matthew Fuhrmann and Sarah E. Kreps, ‘Targeting Nuclear Programs in War and Peace: A Quantitative Empirical Analysis, 1941–2000’ Journal of Conflict Resolution 54/6 (2010) 831–59.

⁴⁰ Muhammet A. Bas and Andrew J. Coe, ‘Arms Diffusion and War’ Journal of Conflict Resolution 56/4 (2012) 651–74.

⁴¹ Sandeep Baliga and Tomas Sjöström, ‘Strategic Ambiguity and Arms Proliferation’ Journal of Political Economy 116/6 (2008) 1023–57.

⁴² Alexandre Debs and Nuno P. Monteiro, ‘Known Unknowns: Power Shifts, Uncertainty, and War’ International Organization 68/1 (2014) 1–31.

⁴³ Garfinkel and Dafoe, ‘How Does the Offense-Defense Balance Scale?’ .

⁴⁴ Heather Williams, ‘Asymmetric Arms Control and Strategic Stability.’

⁴⁵ Caitlin Talmadge, ‘Emerging Technology and Intra-War Escalation Risk’; Jacquelyn Schneider, ‘The Capability/Vulnerability Paradox and Military Revolutions.’

⁴⁶ Shiping Tang, ‘The Security Dilemma: A Conceptual Analysis’ Security Studies 18/3 (2009) 587–623.

⁴⁷ Charles L. Glaser, ‘The Security Dilemma Revisited’ World Politics 50/1 (1997) 171.

⁴⁸ Robert Jervis, ‘Dilemmas About Security Dilemmas’ Security Studies 20/3 (2011) 416. See also Sean M. Lynn-Jones, ‘Offense-Defense Theory and Its Critics’ Security Studies 4/4 (1995) 660–91; Garfinkel and Dafoe, ‘How Does the Offense-Defense Balance Scale?’ .

⁴⁹ Robert Jervis, ‘Cooperation Under the Security Dilemma’ World Politics 30/2 (1978) 167–214.

⁵⁰ Jervis, ‘Cooperation’, 199.

⁵¹ Scott D. Sagan, ‘Nuclear Latency and Nuclear Proliferation’ in Forecasting Nuclear Proliferation in the 21st Century, ed. William Potter and Gaukhar Mukhatzhanova (Stanford Security Studies, 2010), 80–101.

⁵² Michael C. Horowitz, The Diffusion of Military Power: Causes and Consequences for International Politics (Princeton University Press, 2010), 104.

⁵³ Matthew Fuhrmann and Benjamin Tkach, ‘Almost Nuclear: Introducing the Nuclear Latency Dataset’ Conflict Management and Peace Science 32/4 (2015) 443–61.

⁵⁴ Fuhrmann, Atomic Assistance, 2.

⁵⁵ Scott D. Sagan, ‘Why Do States Build Nuclear Weapons?: Three Models in Search of a Bomb’ International Security 21/3 (1996) 57–58.

⁵⁶ Dagobert L. Brito and Michael D. Intriligator, ‘The Economic and Political Incentives to Acquire Nuclear Weapons’ Security Studies 2/3–4 (1993) 303. On the ability of counter-proliferators to break these chains, see Nicholas L. Miller, ‘Nuclear Dominoes: A Self-Defeating Prophecy?’ Security Studies 23/1 (2014) 33–73.

⁵⁷ Kyle Beardsley and Victor Asal, ‘Nuclear Weapons Programs and the Security Dilemma’ in The Nuclear Renaissance and International Security, ed. Matthew Fuhrmann and Adam Stulberg (Stanford, CA: Stanford University Press, 2013), 266, 269.

⁵⁸ Tristan A. Volpe, ‘Atomic Leverage: Compellence with Nuclear Latency’ Security Studies 26/3 (2017) 522.

⁵⁹ The logic of giving up a hostage to send a costly signal comes from Thomas C. Schelling, Arms and Influence (Yale University Press, 1966). See also Evan Braden Montgomery, ‘Breaking Out of the Security Dilemma: Realism, Reassurance, and the Problem of Uncertainty’ International Security 31/2 (2006) 153.

⁶⁰ Scott D. Sagan, ‘The Causes of Nuclear Weapons Proliferation’ Annual Review of Political Science 14/1 (2011) 238; Andrew J. Coe and Jane Vaynman, ‘Collusion and the Nuclear Nonproliferation Regime’ The Journal of Politics 77/4 (2015) 983–97.

⁶¹ Sechser, Narang, and Talmadge, ‘Emerging Technologies and Strategic Stability,’ 728.

⁶² Alexander H. Montgomery, ‘Stop Helping Me: When Nuclear Assistance Impedes Nuclear Programs’ in The Nuclear Renaissance and International Security, ed. Adam N. Stulberg and Matthew Fuhrmann (Stanford, CA: Stanford University Press, 2013), 177–202; Andrea Gilli and Mauro Gilli, ‘Why China Has Not Caught Up Yet: Military-Technological Superiority and the Limits of Imitation, Reverse Engineering, and Cyber Espionage,’ International Security 43/3 (2019) 141–89.

⁶³ Robert L. Jervis, The Logic of Images in International Relations (Columbia University Press, 1970), 18.

⁶⁴ Jervis, Logic of Images, 6.

⁶⁵ Steven E. Miller, ‘Cyber Threats, Nuclear Analogies? Divergent Trajectories in Adapting to New Dual-Use Technologies’ in Understanding Cyber Conflict: Fourteen Analogies, ed. George Perkovich and Ariel E. Levite (Washington, DC: Georgetown University Press, 2017), 161–79.

⁶⁶ George H. Quester, ‘The Last Time We Were At “Global Zero”’ Naval War College Review 64/3 (2011) 6.

⁶⁷ R. Scott Kemp, ‘The Nonproliferation Emperor Has No Clothes: The Gas Centrifuge, Supply-Side Controls, and the Future of Nuclear Proliferation’ International Security 38/4 (2014) 39–78.

⁶⁸ Joseph M. Parent and Sebastian Rosato, ‘Balancing in Neorealism’ International Security 40/2 (2015) 55.

⁶⁹ Stephen Van Evera, Causes of War (Ithaca, NY: Cornell University Press, 1999).

⁷⁰ Charles L Glaser, Rational Theory of International Politics: The Logic of Competition and Cooperation (Princeton, N.J: Princeton University Press, 2010), 75.

⁷¹ Albert Wohlstetter, ‘Perspective on Nuclear Energy’ (Santa Monica, CA: RAND Corporation, 1968); Toby Dalton et al., ‘Toward a Nuclear Firewall: Bridging the NPT’s Three Pillars’ (Washington, DC: Carnegie Endowment for International Peace, 2017).

⁷² Baliga and Sjöström, ‘Strategic Ambiguity and Arms Proliferation’; Robert S. Litwak, ‘Living with Ambiguity: Nuclear Deals with Iran and North Korea,’ Survival 50 (2008) 91–118.

⁷³ John J. Mearsheimer and Stephen M. Walt, ‘Leaving Theory behind: Why Simplistic Hypothesis Testing Is Bad for International Relations’ European Journal of International Relations 19/3 (2013) 427–57.

⁷⁴ To conduct covariation tests, for instance, we must first determine the impact of additive manufacturing on the development of nuclear technology and then measure dual-use distinguishability over time. See Robert Adcock and David Collier, ‘Measurement Validity: A Shared Standard for Qualitative and Quantitative Research’ American Political Science Review 95/3 (2001): 529–46.

⁷⁵ Shaw et al., ‘Evaluating WMD Proliferation Risks’, 7.

⁷⁶ Alexander H. Montgomery and Adam Mount, ‘Misestimation: Explaining US Failures to Predict Nuclear Weapons Programs’ Intelligence and National Security, 29/3 (2014) 357–86.

⁷⁷ Hoffman and Volpe, ‘Internet of Nuclear Things’, 105.

⁷⁸ Hoffman and Volpe, 102.

⁷⁹ Hoffman and Volpe, 102.

⁸⁰ Hoffman and Volpe, 103.

⁸¹ For an overview in the context of non-proliferation policy, see James Acton, ‘On the Regulation of Dual-Use Nuclear Technology,’ in Governance of Dual-Use Technologies: Theory and Practice, ed. Elisa Harris (American Academy of Arts and Sciences, 2016). See also Miller, ‘Cyber Threats, Nuclear Analogies?’.

⁸² Eliza Gheorghe, ‘Proliferation and the Logic of the Nuclear Market’ International Security 43/4 (2019) 88–127.

⁸³ Volpe, ‘Atomic Leverage’; Matthew Fuhrmann, ‘The Logic of Latent Nuclear Deterrence,’ SSRN Scholarly Paper (Rochester, NY: Social Science Research Network, 8 September 2017); Rupal N. Mehta and Rachel Elizabeth Whitlark, ‘The Benefits and Burdens of Nuclear Latency’, International Studies Quarterly 61/3 (2017): 517–28. On proliferation strategy, Narang, ‘Strategies of Nuclear Proliferation’; Dan Altman and Nicholas L. Miller, ‘Red Lines in Nuclear Nonproliferation’ The Nonproliferation Review 24/3–4 (2017) 315–42.

⁸⁴ For a full articulation of this argument, see Hoffman and Volpe, ‘Internet of Nuclear Things.’