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In February 2023, United Nations Secretary General António Guterres issued a public warning: “We are at the highest risk in decades of a nuclear war that could start by accident or design.” He followed with a call to action: “The so-called ‘tactical’ use of nuclear weapons is absurd. Nuclear-armed countries must renounce the use of these unconscionable weapons – anytime, anywhere.”¹

In stark contrast, this spring, Belarusian President Aleksandr Lukashenka proudly announced that tactical nuclear weapons from Russia “more powerful than those dropped on Hiroshima and Nagasaki” had arrived to be stationed in his country.²

These events are part of an increasing focus on tactical nuclear weapons in various corners of the globe—both for their perceived utility and their dangers. The statements above showcase that we are at an inflection point that will shape the international security environment for decades. Can the world end tactical nuclear weapons, or are we doomed to their expansion?

To be sure, the latter path sharply raises the risks of nuclear weapons being used, whether intentionally in conflict or from the serious miscalculations that can occur in the fog of war.

The myriad security challenges shaping the global security environment today have given rise to some experts and officials calling for a ramp-up in tactical nuclear weapons and a return to the wider deployment of these systems that characterized the Cold War.

We argue the opposite. The vast and complex security threats that exist in the world today make tactical nuclear weapons even more dangerous than they were during the last century—a landscape where many types of these weapons were deployed in multiple regions, poised for use in escalating battle across the nuclear threshold. Rather than contributing to strategic deterrence, we believe that tactical nuclear weapons actually undermine it—by enabling a lower threshold for nuclear weapons use through deploying weapons with a relatively lower yield which are sometimes erroneously portrayed as being “smaller” and thus more “acceptable,” “credible,” or potentially “controlled,” despite their enormously destructive potential.

The strategic and practical reasons that most nuclear-armed nations reduced, retired, and avoided deploying tactical nuclear weapons still hold today, and are perhaps even more important to nations navigating the current security environment than during the Cold War. We aim to show this by highlighting the history of tactical nuclear weapons across five nations—the United States, Russia, China, the United Kingdom, and France (the five treaty-accepted nuclear weapon states under the Nuclear Nonproliferation Treaty, or NPT)—and the reasons that these nations made incredible progress in reducing these nuclear capabilities around the world. The best path from the current inflection point is for the same nations to pursue further reductions and hopefully an end to these types of nuclear weapons.

This review contains three main chapters.

What is a Tactical Nuclear Weapon? A short description of what we, the authors, classify as tactical nuclear weapons, and notes regarding other commonly-used terms.

A Brief History of the Rise and Decline of Tactical Nuclear Weapons. In order to illuminate the policy path forward, this chapter presents a brief and clarifying history of how nuclear nations drove a dangerous expansion in tactical nuclear weapons, but then made significant progress for decades in moving away from these weapons capabilities due to military and technical decision-making, recognition of their unique risks, and geostrategic reasons. We describe how this brought the world toward a landscape mostly dominated by nuclear-armed nations narrowing their roles to strategic deterrence purposes. However, this chapter also shows that the world is at an inflection point from which nations’ actions could lead either to the further decline of these weapons or another Cold War-like expansion of them.

Recommendations For Ending Tactical Nuclear Weapons. Finally, taking lessons from this history and from the worrying trends of today, we recommend that countries prioritize finding ways to reduce the risks of tactical nuclear weapons, and move toward their end as an urgent priority.

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In reality, all nuclear weapons are strategic weapons, as any use of them would have strategic impacts and fundamentally change the character of a conflict. Yet, some nuclear systems are designed for potential use as part of a theretofore-conventional conflict. Through the nuclear age, many nations possessing these weapons have designed them with specific conflict utility in mind: demolition to help slow advances of opposing forces, air defense against another nation’s incoming nuclear bombers, to sink enemy ships, and more.

In the early decades of the Cold War, the nuclear weapons possessing nations of that era—the United States, United Kingdom, France, Soviet Union, and People’s Republic of China—developed several dozen types of tactical nuclear weapon capabilities. These weapons were generally, but not exclusively, lower-yield compared to other nuclear weapon capabilities being developed during the heights of the Cold War arms race. These weapons were often characterized as “theater” nuclear weapons (because their relatively shorter range meant they could only be used against targets in the theater where they were located), some as short- or intermediate-range systems, and other specialized devices ostensibly meant for a battlefield.

Still, definitions for tactical nuclear weapons systems can vary. For this analysis, we considered certain nuclear capabilities to be tactical based on several factors, including:

• Exclusion of these weapons in past treaties (i.e., where certain types were omitted as “non-strategic,” tactical, or otherwise not counted as strategic nuclear weapons)
• Intentions of the possessor nations, based on what is publicly known—the declared or assumed mission for a given weapon system
• How other countries likely interpret these nuclear capabilities
• Who would likely request their use—a battlefield or theater commander or one located outside of theater not directly involved in tactical decisions

In the text and graphics within this report, we also characterize some systems as “hybrid.” This designation is meant to indicate that certain capabilities have a blend of potential tactical intent or utility (either by the possessing nation or highly likely to be interpreted as such by other nations), and strategic intent (i.e., deterring nuclear attacks) even if they were not included in past treaties that limited strategic nuclear weapons.

Countries, and even different agencies and communities within those countries, vary in the terms they use. A February 2023 U.S. State Department report on Russian weapons acknowledges the lack of legal definitions for the terms tactical and non-strategic. For its purposes, the State Department does not currently use the term tactical “because the United States does not envision any use of nuclear weapons to be tactical in character or effect.”³

In France, systems analogous to what are considered tactical or non-strategic elsewhere were purposefully called “pre-strategic” starting in 1984, so as to “indicate their desired linkage to strategic nuclear arsenals rather than to conventional theater forces.”⁴ In effect, these nuclear weapons were intended only to be deployed under a last-warning concept, to generate “a significant military effect to force the enemy to take notice and reflect” with the goal being “to give a clear warning of the imminent passage to the strategic nuclear level” if the opposing forces did not alter their actions that had driven a conflict to that level.⁵

Definitions and terminology have evolved over time along with the strategic landscape, changes in conventional military capabilities, the expansion of international cooperation and treaty alliance relationships, the rise of nuclear arms control in the mid-to-late 1900s, and other drivers.

Under the various terms used to describe them, the story of tactical nuclear weapons starts at the very beginning: the era during and immediately after the world wars. Chemical and biological weapons were used in these early decades of the century, and several nations sprinted to weaponize the atom as well. The first uses of nuclear arms in conflict were delivered by the United States against Japan in 1945.

After World War II, multiple nations expected that the next great war could be imminent, and that it would likely entail nuclear attacks launched against them via land, air, and sea. As such, the world entered a period of four nations engaging in concerted planning for nuclear attacks on their territories and those of their allies—how to stop such attacks, including with their own nuclear weapons, and possibly how to use nuclear weapons in combat.

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To fully understand the current risks associated with tactical nuclear weapons, and to best inform policies for addressing those risks, it is important to understand the context in which several nations surged to develop and deploy dozens of types of these weapons and the uses for which they were envisioned. It is perhaps even more important to understand the unique risks and challenges that tactical nuclear weapons entail, and the multiple factors that drove momentum in the opposite direction and led some countries to restrain from developing them in the first place.

Figure 1: All types of in-service nuclear weapons systems of the P5 countries by year, showing the difference between strategic, hybrid, and tactical systems. Tactical and hybrid systems constituted the bulk of the Cold War arms race in terms of individual types of weapons. Despite a sharp drawdown after the fall of the Soviet Union, the number tactical and hybrid systems are again rising.

It is a history characterized by an initial surge of development, followed by decades of decisions to reduce and retire most of these weapons for military, technical, and political reasons, as decision-makers in many nations realized that tactical nuclear weapons were unhelpful in achieving key goals, could undermine strategic objectives, and could increase catastrophic risk to intolerable levels.

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The Early Rise of Tactical Nuclear Weapons (1945–1960s)

From the dawn of the nuclear age to the mid 1960s, four of the first five nuclear-armed nations developed and deployed at least 70 different types of tactical or hybrid nuclear weapon capabilities, from gravity bombs and artillery shells to anti-aircraft and early cruise missiles.⁶

Figure 2A: Number of types of in-service tactical and hybrid nuclear weapons systems of the P5 countries, 1945-1965 highlighted.

The United States led the way in this field. Some of its earliest concepts were nuclear gravity bombs intended for warfighting uses, including improvements on the Little Boy weapon used to devastate Hiroshima. One of the nation’s first tactical nuclear bombs was the Mark 7, a relatively small weapon in size which was designed to look like a fuel tank attached externally on a fighter plane. Its intended tactical utility entailed new design challenges that showed how defense experts envisioned their use: as described in a later publication by Sandia National Laboratories, it required “tactical fuzes and other systems that would permit fighter pilots to deliver nuclear bombs at low altitudes and still escape the blast,” such as the ability to detonate the weapon after it was dropped.⁷