Conventional-Nuclear Integration to Strengthen Deterrence

The United States and its allies should be prepared to fight a conventional war under the nuclear shadow.

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The United States and its allies should be prepared to fight a conventional war under the nuclear shadow. On September 18, the United States and South Korea met for the 23rd ROK-U.S. Integrated Defense Dialogue and issued a joint statement on the need for an enhanced, combined defense architecture through joined planning and execution of conventional-nuclear integration (CNI) efforts through the Nuclear Consultative Group. Recent national defense strategies and the North Atlantic Treaty Organization (NATO) 2022 Strategic Concept identify CNI as a potential solution to adversaries’ increasing consideration of theater nuclear use to win regional conflicts and a part of a broader approach to integrated deterrence. However, there is degree of ambiguity surrounding the definition of CNI, its components, capabilities, and limitations, as well as implications for extended deterrence and assurance.

Conventional-Nuclear Integration

CNI has not been explicitly defined in U.S. national security documents, but broadly speaking, it is the intersection of conventional and nuclear forces to strengthen deterrence. U.S. CNI efforts require conventional forces, operating with nuclear considerations in mind, and nuclear forces that carry out deterrence operations. Those aim to prevent opponents from fielding conventional and unconventional forces and prepare U.S. forces to utilize nuclear strikes within an otherwise conventional conflict. Adversaries more commonly perceive CNI as the merging of conventional and nuclear forces to achieve objectives otherwise unachievable by one force alone.

Following the Cold War, the United States has largely maintained a firebreak between nuclear and conventional capabilities, systems, and strategies, but with some important exceptions like continued U.S. Chemical, Biological, Radiological and Nuclear (CBRN) operations and exercises. However, this long-standing separation is coming under increasing pressure as the United States faces the prospect of regional competition with nuclear-armed adversaries. Russia and China have both invested heavily in theater-range, dual-capable missile systems, allowing them to threaten to employ a nuclear weapon within a regional conflict against the United States and its allies while attempting to remain below the threshold for a strategic nuclear exchange.

Thus, the prevailing question for U.S. analysts arises: How can the United States and its allies disincentivize adversary nuclear use while advancing U.S. regional goals, and what is the U.S. theory for victory if it does fight with conventional or nuclear means? The United States needs a strategy for winning limited regional conflicts with nuclear-armed adversaries and has identified deeper CNI as a potential solution. The U.S. understanding of CNI consists of three major strategy and policy pieces: (1) the need to manage escalation in regional conflicts and deter adversary nuclear use (usually the concern of command-level decisionmakers), (2) the need to develop an integrated series of options to strengthen deterrence, and (3) the need to deny an adversary any advantages gained by nuclear use in a regional conflict through resiliency and preparedness. The implementation of these includes multiple ways and means of imposing significant costs in the context of a regional conflict with the goal of providing U.S. strategists with the widest possible range of response options, ranging from continuing to wage limited conventional conflict through conventional strikes with strategic effect, and if necessary, a nuclear response.

Some progress has been made on this issue; however, achieving an adequate level of CNI will take continued intense coordination both within the United States and with its allies. Operationalizing CNI remains an important focus of the 2022 Nuclear Posture Review’s (NPR) implementation, however, putting thought into practice will.

How Russia and China Approach CNI

Russian and Chinese capabilities and strategies convey a belief that nuclear weapons can be used in theater to gain strategic advantage in conventional conflicts with the United States or its allies. Both adversaries appear to ascribe to similar theories of victory in limited regional conflicts that leverage the potential for nuclear use and perceived asymmetries of geography and stake to deter U.S. intervention and attempt to fracture U.S.-led alliances. Unlike the U.S. conception of CNI that focuses primarily on maximizing its ability to continue to pursue a conventional war even in a nuclear environment, Russia and China have instead focused on developing capabilities that can increase the credibility of limited nuclear threats without provoking a strategic nuclear response from the United States or its allies.

Russian strategy seeks to manage escalation to deter adversary intervention and aggression, prevent the conflict from expanding geographically, ensure state survival, and provide acceptable terms for conflict termination. Broadly speaking, Russia seeks first to achieve these aims by inducing fear in adversary decisionmakers, followed by increasingly damaging strikes on adversary targets while remaining below the threshold for an escalatory adversary response.

Russia has therefore invested heavily in developing a variety of advanced dual-capable nonstrategic weapon systems to bolster conventional military operations abroad, providing Moscow with the flexibility to manage crisis escalation and allow Russia to fight limited nuclear wars below the threshold for strategic nuclear employment. Russian systems include the 9M729/SSC-8 ground-launched cruise missile, which prompted the collapse of the Intermediate Nuclear Forces treaty, as well as the KH-47M2 Kinzhal air-launched ballistic missile. Both are dual-capable theater-range missile systems with the ability to hold targets in Europe and Asia at risk. Russia also fields several conventional precision-strike missile systems, creating a range of capabilities that offers decisionmakers the flexibility to credibly threaten escalating costs (to include with nonnuclear systems) in regional conflicts while still maintaining a significant buffer between regional and major nuclear war.

New Chinese capabilities provide decisionmakers with a growing range of options in a regional conflict. China is pursuing a variety of dual-use systems that can hold U.S. assets and allies in the region at risk, and currently possesses a large variety of intermediate-range dual-use weapons systems. What China’s strategy is less clear. This raises important questions about how the United States and its allies would handle Chinese nuclear coercion aimed at deterring U.S. or allied intervention during a conflict, as well as the prospect for limited Chinese nuclear use to end a crisis on Chinese terms. In a Taiwan contingency, Chinese theater nuclear forces could deter U.S. intervention, deny the United States the ability to traverse the battlespace, and, if need be, end the conflict on terms favorable to Beijing.

The most recently fielded Chinese systems include the DF-26 intermediate-range ballistic missile as well as the DF-17 hypersonic boost-glide vehicle, with a lack of clarity regarding how many of each are dedicated to conventional or nuclear missions. Furthermore, the China’s People’s Liberation Army Rocket Force deploys conventional and dual-capable brigades together, forcing personnel to learn both nuclear and conventional operations. While China still publicly adheres to a no first-use policy, Chinese officials have privately caveated this policy in cases of conventional attacks on Chinese nuclear forces. This suggests a shift to a conventional-nuclear warfighting concept that provides the People’s Republic of China leadership with new strategic options that will increasingly cast a nuclear shadow over U.S. and allied military operations in the region.

Risks and Advantages of CNI

There are two essential challenges to the integration of conventional and nuclear planning. First, there is the danger of blurring the lines between conventional and nuclear forces through their entanglement (actual or perceived). The NPR emphasizes the limited role nuclear weapons play and that the president will only consider their potential employment in “extreme circumstances.” The integration of conventional and nuclear command and control systems warrants special attention because it could risk an entanglement of conventional and nuclear control. This could happen through platform ambiguity by combining conventional and nuclear systems on different vessels and commands that control several forces. This conventional-nuclear nexus is further complicated through other domain capabilities such as space and cyber, which introduce new dimensions of warfare by enabling the advanced surveillance, communication disruption, and precision targeting that needs to be considered for traditional military planning.

Second, the convergence of conventional and nuclear operations can affect the risk of nuclear escalation and the adversary’s willingness to resort to nuclear use. Effective communication of resolve and restraint to the adversary is challenging. On the one hand, the United States and its allies need to signal willingness to respond swiftly to the use of nuclear weapons. On the other hand, they should also show willingness of restraint if the adversary does not escalate the situation to nuclear use. Understanding how the adversary reacts to Washington’s CNI is crucial. For example, CNI might affect adversaries’ security postures and lead to further build-up of weapons system and more aggressive defense strategies. Any convergence could encourage additional changes in Russian and Chinese nuclear and defense policies.

In contrast, integration can strengthen the overall deterrence posture and manage escalation dynamics in a crisis and shape adversary perceptions of whether limited nuclear use would achieve its aims. Integration could help to signal to and convince adversaries that they cannot escalate their way out of failed conventional aggression against the United States or its allies. Competitors are increasingly considering whether tactical nuclear use can shift a conflict to their advantage and CNI might be a useful tool to deter such escalation.

In addition, investments into CNI can help to advance the resiliency of conventional forces in case of nuclear use through dispersed operational bases (a steadfast component of nuclear deterrence), operational capability in a contaminated environment, and a hardening of C3 systems so they are sufficiently agile, resilient, and staffed. The Department of Defense (DOD) identifies resilient conventional forces as the keystone of this aspect of integrated deterrence, articulating that “the Joint Force must be able to survive, maintain cohesion, and continue to operate in the face of limited nuclear attacks. This form of resilience sends a distinct deterrence message to an adversary—that limited nuclear escalation will not render U.S., Allied, and partner forces incapable of achieving our warfighting aims.” If conventional forces are resilient, the adversary’s limited nuclear strikes will not have decisive, military advantage. For examples, NATO agreed to a new CBRN defense policy at the Madrid Summit in 2022 and Japan announced new investments into the resiliency of its defense facilities to ensure operations during wartime. Especially when allies and adversaries alike question the credibility of a nuclear response from the United States, can conventional resiliency and nuclear options then signal commitment to defending its allies and core interests?

Following this, if conventional resiliency is ensured, then CNI can give decisionmakers more flexibility and reduce the prospects for a limited nuclear war. This flexibility in response provides leaders with several options in reaction to a nuclear or other CBRN attack instead of ordering a massive nuclear counterattack. Especially after a possible nuclear strike on NC3 operations or nuclear forces, having command and force integration can increase response capabilities, providing more flexible and proportional response options. However, there are the named caveats such as entanglement that come with this integration.

CNI, Extended Deterrence, and Assurance

There has been a new focus on integration among the United States and its allies. For example, NATO’s 2022 strategic concept and the communiqué of the Vilnius summit both emphasized the increasing importance of greater coherence between conventional and nuclear components defense posture and the Washington Declaration between the United States and South Korea highlighted the increased cooperation between the conventional and nuclear forces: “the Alliance will work to enable joint execution and planning for ROK conventional support to U.S. nuclear operations in a contingency and improve combined exercises and training activities on the application of nuclear deterrence on the Korean Peninsula.” Despite the rhetorical emphasis, there has not been a comprehensive review of efforts to integrate defense planning and operations with U.S. allies. The NATO concept reaffirmed the “unique and distinct role of nuclear deterrence” in a nod to some ongoing concerns with integration.

The question is whether CNI in allied postures can strengthen deterrence in the first place and achieve old and new objectives if it fails. Essentially, it is in the security interests of the United States and its allies to avert nuclear use, manage escalation, and communicate about a new, shared path to the restoration of deterrence if it fails. An important aspect of CNI is how the ally’s conventional forces contribute to a strong integrated U.S.-allied posture against combined threats that will include an adversary’s conventional and nuclear forces. Providing assurance to U.S. allies requires that all forces can operate in regional conflicts and if necessary, in a nuclear environment. Conventional options to respond to a nuclear attack are an important part of the integration of nuclear and non-nuclear forces.

If integration is a feasible way for more adaptive allied planning in the event of adversarial nuclear use, then the question is if currently, geographic combatant commanders’ plans sufficiently address nuclear threats. Are there gaps and seams with U.S. nuclear plans and is planning synchronized with U.S. allies? Increased CNI in different theaters means the inclusion of theater commanders and allies in planning efforts that seek to better integrate and synchronize conventional forces with U.S. nuclear forces acting in their deterrent role. For example, to better prepare South Korea for a nuclear threat scenario, the alliance announced that ROK military personnel will join DOD courses and trainings, which will focus on how the alliance approaches nuclear deterrence on the Korean Peninsula, including through CNI. If integration is deemed a useful concept, putting it into practice will take continued and improved coordination both within the United States and with its allies.

Effective allied CNI requires improved, joint messaging. President Yoon emphasized a swift and overwhelming response, including the use of U.S. nuclear weapons, in the event of a North Korean nuclear attack, while President Biden’s response was more ambiguous, suggesting the end of the North Korean regime and leaving room for a full range of options within a U.S. response. This example stresses the need for improved, coordinated allied messaging.

CNI can support U.S. assurance to allies if Washington’s nuclear planning is more aligned with allies’ conventional posture. For example, Japan’s recent National Security and National Defense Strategies suggest that Japan’s concerns have shifted from entrapment to abandonment, signaling an increased readiness to strengthen collaboration. In line with the announcement during the U.S.-Japan Security Consultative Committee in Washington in January 2023, the nations’ convergence of their national security and defense strategies signals to the adversary that their joined forces can survive and operate in, around, and through a potential theater nuclear attack.

The evolving geopolitical landscape demands a comprehensive evaluation of CNI as a component of U.S. and allied deterrence strategies. As the United States confronts nuclear-armed adversaries such as Russia and China, disincentivizing adversary nuclear use to advance regional goals becomes increasingly important. While challenges to CNI persist, its enhanced deterrence, resiliency, and response flexibility, are significant. Successful CNI development and implementation will require continued coordination, innovation, and synchronized messaging to ensure that the shadow of nuclear conflict remains a deterrent rather than a reality.

Doreen Horschig is an associate fellow with the Project on Nuclear Issues at the Center for the Strategic and International Studies (CSIS) in Washington, D.C. Nicholas Adamopoulos is a program manager and research associate with the Project on Nuclear Issues at CSIS.

Commentary is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

© 2023 by the Center for Strategic and International Studies. All rights reserved.

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