Policy & Politics Security & Conflict

The Nuclear Spectrum

Much of the public discourse on nuclear security is based on the implications of binary scenarios: a nuclear state versus a non-nuclear one. This approach does not account for the fact that beyond these two positions lies a spectrum of relative nuclear capabilities and characteristics. Factors that determine the position of a state in this nuclear spectrum include the size of its nuclear arsenal, its delivery capabilities, the vulnerabilities of its nuclear infrastructure, and its tactical deployment strategy. The state’s relative position, in turn, produces different security implications.

Daniel Moon is a Foreign Service Officer at the U.S. Department of State.  He graduated from Johns Hopkins SAIS in 2018 with a specialization in International Law and Organizations.

The views and opinions expressed in this article are the author’s own and do not necessarily reflect the official policy or position of the U.S. Department of State or any other agency of the United States government.


Much of the public discourse on nuclear security is based on the implications of binary scenarios: a nuclear state versus a non-nuclear one. This approach does not account for the fact that beyond these two positions lies a spectrum of relative nuclear capabilities and characteristics. Factors that determine the position of a state in this nuclear spectrum include the size of its nuclear arsenal, its delivery capabilities, the vulnerabilities of its nuclear infrastructure, and its tactical deployment strategy. The state’s relative position, in turn, produces different security implications.

Existing academic literature already recognizes the tactical relativity of nuclear weapons capability. Kenneth Waltz noted, for instance, that the tactical chances of eliminating the nuclear potential of a state in pursuit of nuclear weapons are highest during the early stage of its development.[1] The implication is that for the state’s adversary, the perceived feasibility of a decapacitating military action depends on the tactical characteristics of the target state’s nuclear capacity. Nor is the idea of nuclear primacy new. In their 2006 Foreign Affairs article “The Rise of U.S. Nuclear Primacy,” Keir Lieber and Daryl Press described nuclear primacy as “the ability to destroy all of an adversary’s nuclear forces, eliminating the possibility of a retaliatory strike.”[2] Implicit in their discussion is an idea of relativity that is integral to this article: that even within the ranks of nuclear states, there are comparative capabilities. Meanwhile, Matthew Kroenig provides insight into the implications of nuclear relativity on state behavior, noting that advantage in the size of the nuclear arsenal increases the state’s tolerance for risk in a crisis.[3]

Other scholars have analyzed nuclear security on different terms of relativity. Michael Horowitz, for instance, offers a temporal dimension, noting that the nuclear state’s inclination to reciprocate aggression declines over time as its experience with nuclear weapons grows.[4] Vipin Narang argues that effective deterrence can be determined by nuclear postures – national policies that articulate how and when the country would use its nuclear arsenal in a conflict scenario.[5]

This submission contributes to the academic discourse in two ways. First, it offers a nuclear spectrum that incorporates both non-nuclear and nuclear positions that a stay may occupy, based largely on tactical capabilities. Second, it borrows the lens of the security dilemma to look at characteristics besides the sheer size of the nuclear arsenal that may inform these capabilities.

The Spectrum

This article identifies six major positions on the nuclear spectrum that a state may occupy:

  • Non-nuclear: the state is not in possession of nuclear weapons, nor is it in pursuit of nuclear weapons.
  • Early development: the state is in pursuit of nuclear weapons, evidenced by the construction of uranium enrichment facilities and centrifuges, and attempts to enrich uranium beyond the necessary concentration level for civilian use; its intentions may not be clear to other states.
  • Late development: the state is in possession of highly enriched uranium (HEU) with a concentration level of 20% or more (theoretically capable of use for weapons),[6] while indicating a clear intention of developing nuclear weapons.[7]
  • Nuclear nascent: the state is in possession of at least one nuclear weapon capable of striking an adversary, but is vulnerable to decapacitation by hostile military action (conventional or nuclear); in other words, the state does not possess reliable nuclear deterrence.
  • Nuclear capable: the state is in possession of nuclear weapons but lacks the ability to eliminate a potential enemy’s retaliatory capability (same as nuclear nascent state); at this stage of the nuclear spectrum, however, its nuclear arsenal is secure from a hostile first-strike and is capable of imposing intolerable retaliatory costs on the enemy, presenting a reliable nuclear deterrence.
  • Nuclear primacy: the state is in possession of nuclear weapons and is capable of eliminating an adversary’s retaliatory capability through a first-strike.

Figure 1: Logic of the Nuclear Spectrum

Daniel Moon

Waltz provides one dimension to the logic of the spectrum: tactical vulnerability. Specifically, assuming that the adversaries of a given state are opposed to its nuclear development, the adversaries will assess the viability of eliminating the state’s nuclear potential through offensive measures. The logic here is that the more tactically vulnerable a state’s nuclear infrastructure is, the more tempted the adversaries are to take action in order to reverse the state’s pursuit of nuclear weapons before the window of opportunity closes. One may thus conclude that countries in the process of nuclear weapons development, particularly in the early stages, are the most likely targets of hostile actions, creating uncertainty and instability.

The concept of relative tactical vulnerabilities also applies to states in possession of nuclear weapons. A country’s leadership that perceives its security interests compromised by a nuclear adversary will likely perceive higher tactical chances of eliminating the adversary’s nuclear arsenal if it is relatively small and vulnerable to military strikes, as is the case with a nuclear nascent state. If the nuclear buildup continues, however, the state becomes nuclear capable, where enough of its arsenal can survive a military first strike and in turn provide reliable nuclear deterrence. Meanwhile, the distinction between a nuclear capable state and one in nuclear primacy is that in the latter position, the nuclear state possesses both reliable deterrence as well as the qualitative and quantitative striking capability to eliminate an adversary’s deterrence, be it nuclear or conventional. This offensive capability introduces instability by virtue of the adversary’s deterrence becoming null.

Thus, we arrive at one plausible explanation for why different positions on the spectrum present different levels of regional and global stability: the tactical vulnerability of the state’s nuclear capacity creates uncertainty, inviting varying levels of hostility from its potential adversaries. Conversely, the nuclear striking capability of a state may be sufficient to eliminate the adversary’s deterrence, which also introduces uncertainty and instability.


Besides tactical characteristics, perception may also shed light on varying levels of stability produced by different nuclear positions. More specifically, how might an adversary perceive the intentions of a nuclear or nuclear-developing state under the analytical framework of the security dilemma? Robert Jervis famously noted that if a country’s security measures are defensive in nature, potential adversaries will not perceive substantial threat to their security.[8] Military hardware or infrastructure would be considered defensive if it were immobile and lacked the ability to “penetrate the enemy’s land,” and were solely applicable to the defense of one’s own territory; examples include Russia’s adoption of a different railroad gauge in order to prevent foreign invasions.[9] What of nuclear weapons? Keir Lieber contends that nuclear weapons are defensive in nature, based on the comparative costs of offensive and defensive deployment:

Offense-defense theory codes nuclear weapons as defense dominant because it is relatively easier and less costly for states to maintain a retaliatory capability than to build a force capable of taking away another’s retaliatory capability.[10]

But if nuclear weapons are indeed defensive in nature, why have states displayed adamant hostility towards the notion of a nuclear Iran or North Korea? While Iran and North Korea may view nuclear weapons as defensive leverage, their potential adversaries perceive the nuclear development as an attempt by Iran or North Korea to upset the status quo balance of power, a necessary prelude to an offensive foreign policy stance. In a global climate in which the normative values surrounding nuclear weapons development have shifted from those of “prestige and legitimacy” in the 1960s to that of abhorrence and suspicion (hence the new, modern norm of joining the “club of nations adhering to the NPT”), it becomes increasingly difficult to argue that potential adversaries will not view a state’s nuclear development as anything but hostile and offense-driven.[11] Thus, a state in late development or a nuclear nascent state will be viewed as pursuing an offensive strategy by adversaries, while a state in early development will be viewed with uncertainty, due to ambiguity towards whether the state if pursuing a civilian or military nuclear program.

But what about perceptions toward a nuclear capable state? The main distinction between a nuclear nascent and a nuclear capable state is that the latter possesses reliable second-strike capability. The logic behind labeling the intentions of a nuclear capable state as defensive rather than offensive is that the development of second-strike capability must have involved some defensive measures by the state against potential first-strike scenarios, signaling to its potential adversaries that its nuclear posture is more defense-oriented. The problem here, of course, is whether the state’s defensive nuclear measures are indeed viewed by adversaries as defensive.

One may speculate, for instance, that one of the reasons the American and Soviet leaderships pursued a ceaseless nuclear arms race for most of the Cold War – despite their mutual understanding by the 1960s that they both possessed reliable retaliatory capabilities[12] – may be due to the fact that the American and Soviet second-strike capabilities were heavily contingent on weapons systems and technology that were often ambiguous in their defensive/offensive nature: building up nuclear stockpiles in the thousands, developing delivery systems with longer range and precision, and producing long-range bombers and submarines capable of nuclear strikes are just a few examples of deterrent measures adopted by a state that could well be perceived as offensive by an adversary.

Meanwhile, China’s nuclear deployment strategy presents an interesting point of contrast. The 2008 earthquake in the Sichuan Province, as devastating as it was, revealed a key characteristic about China’s nuclear strategy. Following media reports that showed strangely collapsed hills and teams of radiation technicians rushing towards the disaster site, the Chinese military admitted in late 2009 that it had built a network of tunnels that allegedly stretches over 3,000 miles for the housing its nuclear weapons.[13] In the 2011 Annual Report to Congress, the U.S. Department of Defense acknowledged the existence of an “obscure tunnel network, which reportedly stretches over 5,000 km” that has been developed by China’s strategic missile force, the Second Artillery Corps.[14] Disregarding the political ramifications of the tunnel system, let us examine the role of this tunnel network in the framework of the security dilemma. Unlike bombers or missiles, a nuclear tunnel network is arguably defensive in nature, since it holds no significant tactical value for a first-strike move. Instead, the tunnel network provides defensive value by allowing the nuclear state to effectively hide and shield its nuclear arsenal from a first-strike. In essence, second-strike capability functions fully well as defensive deterrence when the characteristic of that capability is such that it is defense-oriented. In fact, Gregory Kulacki from the Union of Concerned Scientists suggested that the defensive nature of the nuclear tunnel network in China nullifies the pressure to engage in an arms race: “With more tunnels and a better chance of survivability, they may think they don’t need as many warheads to strike back.”[15]

Of course, this is not the case for a state in the position of nuclear primacy, which possesses enough nuclear capability to eliminate a potential enemy’s retaliatory capability with a first-strike. In an environment where second-strike is no longer at play, offensive suspicion reemerges, whereby states begin to view a nuclear state pursuing or occupying the position of nuclear primacy as seeking an offensive foreign policy.


The analysis above paves the way for the following conclusion: once a state begins to develop nuclear weapons, its impact on regional and global stability depends on such factors as the tactical vulnerability of the state’s nuclear capacity and outside perceptions toward the state’s nuclear intentions. The tactical vulnerability decreases as the state inches toward nuclear maturity, but other states perceive the country’s nuclear intentions as defensive only when the country is nuclear capable, where the country lacks the ability to eliminate an adversary’s retaliatory capability with a first-strike but possesses defensive second-strike capability to deter aggression. The below graph demonstrates fluctuating levels of stability along the spectrum (Implicit in my conclusion is that perception of nuclear intention plays a larger role in. determining stability than the objective tactical vulnerability of a state’s nuclear capacity.)

Figure 2: The Nuclear Spectrum

Nuclear Spectrum

According to this framework, a static international community inhabited exclusively by nuclear capable states would be the most ideal scenario to produce stability. In reality, the world today has a wide distribution of nuclear capabilities along the spectrum, with some states moving toward other positions. The P5 of the UN Security Council could be characterized as nuclear capable (with the United States having some claim toward nuclear primacy in the years following the Cold War), while North Korea may be viewed as nuclear nascent.

In other words, a community of nuclear capable states may be the most ideal for international stability, but the process of getting to that point – possibly through individual efforts by non-nuclear states to become nuclear capable – would involve many states transitioning through disruptive nuclear spectrum positions, such as the late development stage.

This nuclear spectrum by no means provides an explanation for global nuclear security with pinpoint accuracy. Much of the logical buildup relies at times on simplifications that warrant in-depth research. It may be the case that there are additional nuclear positions along the spectrum that need to be defined. In addition, there are new dimensions to military actions – such as cyber capabilities – that affect the state’s nuclear capability. Nonetheless, if there is any value in this article, it is in providing a conceptual framework through which one may analyze the ongoing nuclear security issues around the globe.


[1] Kenneth Waltz. “The Spread of Nuclear Weapons: More May Be Better.” Conflict After the Cold War. Ed. Richard Betts. Pearson Education, Inc. 2008. 457.

[2] Keir Leiber and Daryl Press. “The Rise of U.S. Nuclear Primacy.” Foreign Affairs, Volume 85, No. 2. 2006.

[3] Matthew Kroenig. “Nuclear Superiority and the Balance of Resolve: Explaining Nuclear Crisis Outcomes.” International Organization, Volume 67, No. 1. 2013.

[4] Michael Horowitz. “The Spread of Nuclear Weapons and International Conflict: Does Experience Matter?” The Journal of Conflict Resolution, Volume 53, No. 2. 2009.

[5] Vipin Narang. “What Does It Take to Deter? Regional Power Nuclear Postures and International Conflict.” The Journal of Conflict Resolution, Volume 57, No. 3. 2013.

[6] Sharon Squassoni, Stephanie Cooke, Robert Kim, and Jacob Greenberg. “Governing Uranium in the United States.” Center for Strategic and International Studies. March 6, 2014. 26.

[7] Concerning the 20% threshold, there are two points of clarification to make: 1) In addition to the concentration threshold, the International Atomic Energy Agency (IAEA) specifies approximate threshold quantities (in kilograms) of uranium required for production of a nuclear explosive device for different kinds of isotopes, but in this paper, I will look only to the concentration threshold as an indicator sufficient enough to suggest the state’s nuclear intentions; 2) Given that there are cases where HEU are used for civilian and research purposes rather than for the development of nuclear weapons, it would also be necessary to observe the political and security context in which the enrichment process is taking place in order to understand the state’s intentions.

[8] Robert Jervis. “Cooperation Under the Security Dilemma.” Conflict After the Cold War. Ed. Richard Betts. Pearson Education, Inc. 2008. 415.

[9] Ibid. 424-425.

[10] Keir Lieber. “Grasping the Technological Peace: The Offense-Defense Balance and International Security.” International Security, Volume 25, No. 1. 2000. 96-97.

[11] Scott Sagan. “Why Do States Build Nuclear Weapons? Three Models in Search of a Bomb.” International Security, Volume 25, No. 3. 1996. 76.

[12] Lieber. 98.

[13] William Wan. “Georgetown students shed light on China’s tunnel system for nuclear weapons.” The Washington Post. November 29, 2011.

[14] Office of the Secretary of Defense. Annual Report to Congress: Military and Security Developments Involving the People’s Republic of China. 2011.

[15] Wan.

By Daniel Moon

Daniel Moon is a Foreign Service Officer at the U.S. Department of State. He graduated from Johns Hopkins SAIS in 2018 with a specialization in International Law and Organizations.