Nuclear deterrence and the mission of those who work on the nuclear enterprise have never been far from my mind since I first worked in the Pentagon in 1981. In those Cold War days, when nuclear weapons and the need for deterrence often made newspapers headlines here and abroad, one of my first defense-related jobs was working as a physicist on missile defense and the then-current but infeasible Strategic Defense Initiative, and on basing options for the Missile Experimental (MX), which ultimately became the Peacekeeper ICBM. Later, after the end of the Cold War, I ran the Pentagon’s Nunn-Lugar program, which removed and eliminated nuclear weapons in Russia, Ukraine, Kazakhstan, and Belarus.

While much has changed in the more than 35 years since I first served in the Pentagon, nuclear deterrence remains crucial to our nation’s defense and to strategic stability. Even if nuclear weapons fortunately make fewer headlines than they did during the Cold War and immediate post-Cold War days, the people, capabilities, and systems that comprise America’s nuclear force remain the bedrock of the nation’s security. In light of dramatic changes in the nuclear security environment against an unchanged backdrop of the terrible destructiveness of nuclear weapons and the ineffectiveness of defenses against them, the Defense Department took steps in recent years, culminating in my time as Secretary of Defense from 2015 to 2017, to recapitalize the nation’s nuclear force to ensure safe, secure, and effective deterrence well into the future.

These investments and this recapitalization are not intended to stimulate competition with anyone else; and it is clear they are not having that effect. Indeed, those worried about the start of a new arms race miss the lesson of the past two decades: Despite decades of American and allied reserve—for 25 years our nations have refrained from building anything new—many countries, including Russia, North Korea, and more, have been doing just that. And some of these nations are even building some new types of weapons. So those who suggest that the U.S. recapitalization is a major stimulus to other powers to build more do not have the evidence of the past 25 years on their side.

The Enduring Role of Nuclear Deterrence

It is a remarkable achievement that in the more than seven decades since August 1945, nuclear weapons have not been used again in war. But that is not something that can ever be taken for granted. Nuclear weapons remain the single most fearsome and dangerous technology created by humankind. And for that reason, the Defense Department’s highest priority mission is nuclear deterrence. To that end it has long devoted enormous resources, thought, and energy to prevent their use in war.

In all the years since the Manhattan Project, no one has ever found a perfect defense against these weapons. As a result, only through our own nuclear enterprise can we hope to deter nuclear attacks that would result in enormous devastation. Deterrence is a simple concept, at once elegant and crude, but it rests on a complicated, human-intensive, and technology-intensive system of systems. As a result, the Defense Department dedicates some of its best people and most advanced technology to this mission.

As to the human inputs, thousands of men and women across the country, in uniform and as civilians, contribute to the nuclear deterrence mission. The workforce that keeps the nation’s nuclear enterprise safe, secure, and effective is composed of operators, enablers, maintainers, planners, communicators, security forces, engineers, and facilities personnel on Defense Department bases and installations; scientists, engineers, and technicians in the Department of Energy weapons labs; and many more, including in the defense industry. Each member of that workforce is key to the nation’s deterrence effort.

Technologically, there are also many different pieces to this system. It is built on the bedrock of the “triad:” the nation’s ICBMs, bombers, and sea-launched ballistic missiles.¹ Just as critical to the mission is the network of capabilities that enable nuclear command and control, communications, and integrated tactical warning and attack assessment—satellites, radar systems, ground stations, command posts, control nodes, communications links, and more—that ensure the triad all works assuredly but only on command, and cannot misfire either by mistake or by the deliberate act of a malevolent insider.

Together, this system of systems provides the one person whom the nation has entrusted with the immense nuclear decision-making responsibility—the President of the United States—the best possible picture of information, so that the President can make the most informed decision possible to keep our country safe and prevent nuclear war. The confidence—of Presidents and Washington policymakers, the nation’s allies and partners, and our potential adversaries—that every part of this system is working as smoothly as it should is what makes nuclear deterrence effective. Ensuring that knowledge demands unparalleled excellence from every person involved with the Defense Department’s nuclear force.

Much has changed since the end of the Cold War, and for that we can be grateful. Through extensive negotiations with Russia, the U.S. nuclear stockpile is 85 percent smaller than it was at its Cold-War peak. And in today’s security environment, which is dramatically different from that of the past generation and still more different from the generation before that, the United States faces a nuclear landscape that continues to evolve. Many of these changes, however, are adverse, and are also less predictable going forward than during the Cold War.

One feature of the landscape that has assuredly not changed is the nature of nuclear deterrence itself: It still depends on the perception of America’s potential adversaries about our will and ability to act. At a strategic level, the Defense Department’s nuclear forces are still intended to deter large-scale nuclear attack against the United States. And U.S. security commitments to our allies in the Asia-Pacific, the Middle East, and Europe, and as part of the North Atlantic Treaty Organization (NATO) have not altered.

The nuclear posture also continues to do much more. It contributes to convincing potential adversaries that they will not be able to escalate their way out of a failed conventional aggression. It helps ensure that, in a regional conflict, a losing state will not be tempted to build and escalate to nuclear weapons use in order to cause the United States and its allies to back down. The U.S. nuclear posture also assures allies that extended deterrence guarantees are credible, which enables many of them to forgo developing nuclear weapons themselves, despite their own strategic predicaments and the relative technological ease of developing these weapons. And should deterrence ever fail despite our best efforts, the Defense Department’s nuclear posture provides the President with options to achieve U.S. and allied objectives, a responsibility that every President must take with the utmost seriousness.

In some other respects, however, today’s nuclear landscape is dramatically different than it was during the Cold War. Our deterrent must adapt accordingly to continue to preserve strategic stability and nuclear restraint in this new landscape and ensure that the threshold for nuclear use does not lower.

While the United States has built no new types of nuclear weapons or delivery systems for the past 25 years, and while our allies in Asia, the Middle East, or NATO have not either, many other states have done just that. Russia has long been a nuclear power, but Moscow’s recent saber-rattling and building of new nuclear weapons systems raises serious questions about its leaders’ commitment to strategic stability, their regard for the long-established abhorrence of the use of nuclear weapons, and their respect the profound caution that Cold War-era statesmen—Russian and American alike—showed with respect to brandishing nuclear weapons.

Russia is investing in new ballistic missile submarines, heavy bombers, and the development of a new ICBM. These investments by themselves would not be novel, even if they necessitate continued, strong American deterrence. But they are also paired with novel concepts for how nuclear weapons could be used and some entirely new and even bizarre types of nuclear weapons systems, suggesting an increase in Russia’s reliance on nuclear weapons in its strategic planning instead of the decrease that the United States has long sought.

Meanwhile, North Korea continues to proceed with a 15-year breakout of nuclear weapons and missiles that will likely pose an increasing threat to the United States and its allies. North Korea has conducted tests of land-based ballistic missiles and submarine-launched ballistic missiles. It continues to develop its KN08 road-mobile ballistic missile, which, while still untested, could become capable of delivering a warhead to the continental United States. And in 2016 alone, North Korea conducted its fourth and fifth nuclear tests.

In view of North Korea’s breakout, the United States and its allies have continued to build more robust ballistic missile defenses to stay ahead of the North Korean threat, including deploying additional and improved Ground-Based Interceptors in Alaska, and agreeing with our Korean allies to deploy the Terminal High-Altitude Area Defense system, or THAAD, in the Republic of Korea, enhancing existing defenses in the Republic of Korea, Japan, Guam, and afloat. While not a perfect protection against nuclear attack, missile defenses contribute to deterrence by complicating the analysis of a potential adversary that a nuclear attack will succeed. The United States must continue to back up those defenses against North Korean missile attack with extended deterrence: the commitment that any attack on America or its allies (in this case South Korea and Japan) will not only be defeated, but that any use of nuclear weapons will be met with an overwhelming and effective response. The United States also maintains ever-improving conventional defense forces on the Korean Peninsula, which reinforce South Korean forces that also continue to improve.

Russia and North Korea are two countries that, albeit very different in kind and capabilities, stand out in today’s evolving nuclear landscape. There are others as well. While China has generally conducted itself professionally in the nuclear arena, refraining from saber rattling, at the same time it has increased its arsenal in both quality and quantity. China is developing a road-mobile ICBM capable of carrying multiple reentry vehicles, an intermediate-range ballistic missile that will likely have both nuclear and conventional variants, and it is constructing an additional nuclear-powered ballistic missile submarine to join the four that it has already commissioned.

Iran’s nuclear aspirations have been constrained at least temporarily, and transparency over its activities has been increased, by the 2015 nuclear accord. The Joint Comprehensive Plan of Action, as long as it continues to be implemented and honored, will verifiably prevent Iran from acquiring a nuclear weapon.

India has shown responsible behavior with its nuclear technology generally over several decades but continues to expand its arsenal. Pakistan’s nuclear weapons, meanwhile, are entangled in a history of tension with India. The United States works with Pakistan to ensure stability, yet its nuclear arsenal also continues to grow in scale and scope. As the breakup of the Soviet Union and the subsequent Nunn-Lugar program illustrate, in all states and emphatically in Pakistan, both internal political turmoil and command-and-control shortcomings are a constant source of danger.

Despite the actions of some states, today’s nuclear environment is not nearly as bad as it might have been. Indeed, non-proliferation and arms control initiatives, including President Obama’s Nuclear Security Summits and the Nunn-Lugar program, have slowed the wider spread of nuclear weapons and prevented the dangers of loose nuclear weapons. Such actions have contributed measurably to the nuclear peace that uneasily settled over the world in 1945.

Nevertheless, the changing nuclear landscape and significant investments by many other countries in new nuclear weapons systems pose challenges to that peace. While other actions in defenses and non-proliferation are critical, it will also be necessary to ensure nuclear deterrence on behalf of the United States long into the future. To that end, the United States must stay the course on the plan of correcting decades of underinvestment in its nuclear deterrent dating back to the end of the Cold War, when funding for the nuclear enterprise dropped dramatically.²

Over the past 25 years, the United States made only modest investments in basic nuclear sustainment, life-extension, and operations. The Department of Defense nuclear enterprise funding remained fairly constant during this period, roughly $15 billion per year in an annual overall defense budget now at about $580 billion. But almost all of this money has been devoted to the manning and maintenance of Cold War systems, not to investment in recapitalization of existing stores, let alone new types of systems. In consequence, many of the U.S. arsenal’s capabilities have aged.

Indeed, in the coming decades, the military’s bombers and 1970s-era ICBMs will reach the point at which their lifespan can no longer be extended. At nearly thirty years old, the B-2 bomber is the newest system in the U.S. triad. The air-launched cruise missile is already decades beyond its planned service life, its reliability is degrading, and its viability is increasingly challenged by advanced air defenses. And the nation’s nuclear-armed submarines will irreversibly age out of service beginning in 2027.

Looking back, it is clear that we were right to choose not to maintain the massive arsenal or the level of spending on nuclear forces of the Cold War years. But it is just as apparent that the Defense Department cannot further defer recapitalizing Cold-War era systems if we are to maintain a safe, secure, and effective nuclear force that will continue to deter potential adversaries that are making improvements in their air defenses and their own nuclear weapons systems. The choice is not between replacing these platforms or keeping them, but rather between replacing them and losing them altogether. The latter outcome would, unfortunately, result in lost confidence in our ability to deter. The United States cannot afford this in today’s security environment or in any reasonably foreseeable future security environment.

Even more troubling than the aging of the physical elements of the nuclear enterprise were signs that the Defense Department had not been treating the nuclear mission as its highest priority. Both an independent and an internal review of the nuclear enterprise conducted in 2014 indicated gaps between what leadership expected of the nuclear force and what the Defense Department was doing to support the personnel who meet those exceptionally high expectations.³ Indeed, these reviews found that the manning, equipment, and quality of training for the nuclear mission did not always meet standards required for the Defense Department’s highest-priority mission.

A Nuclear Recapitalization Plan

As a result, it had become clear in recent years that the Defense Department required a significant recapitalization effort, one that invested in every element of the triad as well as the people responsible for maintaining the nuclear force at the highest possible levels of safety, efficacy, and efficiency. Beginning with the latest budget proposal of my tenure as Secretary, the Defense Department budget planned to invest a total of $19 billion in 2017, and $108 billion over the five years thereafter, to sustain and recapitalize the nuclear force and associated strategic command, control, communications, and intelligence systems. This funding included increases for manpower, equipment, vehicles, maintenance, technological efforts to help sustain the bomber fleet, and more.

Additionally, the budget also fully funded the first stages of plans to ensure that the capabilities required to sustain nuclear deterrence do not become obsolete. This included replacing old ICBMs with new ones that will be less expensive to maintain; keeping strategic bombers effective at their nuclear as well as conventional missions in the face of more advanced air defense systems, in part by replacing aging air-launched cruise missile with a more effective version called the long-range standoff weapon and in part by completing the new B-21 bomber (which is principally directed toward non-nuclear missions but is nuclear capable); replacing the F-16s in the dual-capable aircraft fleet with F-35s and the B61-12 gravity bomb; and building replacements for the Ohio-class ballistic missile submarines.

Of course, the Defense Department must also ensure that it has the people for its nuclear force to succeed. Therefore, on the recommendation of nuclear enterprise reviews, the Pentagon renewed investments in the people carrying out this mission. For example, during my last year as Secretary, I visited with some of the men and women at Minot Air Force Base where the Department has recently expanded childcare options, kept fitness centers open 24 hours a day, and provided new assignment incentive pay and special assignment duty pay for military personnel. These sorts of improvements are critical because deterrence is not credible unless the Defense Department has the right people to man, equip, operate, secure, and support the nuclear enterprise.

Taking care of the nuclear force’s people and investing in its capabilities will cost money of course, but most people do not realize that funding for the nuclear enterprise is a relatively small percentage of total defense funding. I am confident the nation will make the right investments in the coming years for two reasons. First, if the United States does not replace these systems, quite simply they will age to the point of becoming unsafe, unreliable, and ineffective. Second, while these investments are usually referred to simply as nuclear “modernization,” that’s only true in the sense of sustaining deterrence. None of these investments is intended to change the underlying concept of deterrence or how it works; no one can do that in any event.

In a changing world, the U.S. government and the Department of Defense have begun the process of re-ensuring our nuclear deterrence, the bedrock of the nation’s security. After a quarter-century of investing too little, the Defense Department and I recognized that it has become necessary to take steps to sustain nuclear deterrence, and ultimately ensure that nuclear weapons are never used. Indeed, even as we all wish to live in a world without nuclear weapons, it is also true—as President Obama noted many times—that goal may not be realized within our lifetimes. Even more, given what we see in today’s security environment, it is also likely that our children, and their children, will also live in a world where nuclear weapons still exist.

Thus, although nuclear weapons do not get the same amount or kind of media attention they did when I started my career at the Defense Department three decades ago, they will remain critically important to the nation’s security for years to come. To ensure our deterrence in light of changes in technology and in the nuclear security environment, the Defense Department must continue to take the necessary steps—and make the critical innovations and investments—to ensure safe, secure, and effective nuclear deterrence for decades to come.