America’s strategic nuclear deterrent is nearing a crossroads. On one hand, the size, shape and purpose of the U.S. nuclear arsenal are all up for debate. For over two decades Washington has been shedding excess weapons that were a legacy of the Cold War. Senior officials today are also much more concerned with proliferation and the possibility of nuclear terrorism than great-power brinkmanship or the prospect of a massive nuclear exchange. The confluence of declining defense budgets and looming recapitalization costs has made nuclear programs a potential target for funding cuts.

On the other hand, the Obama administration is currently committed to a number of nuclear modernization efforts, from developing a new penetrating bomber that will eventually supplant the B-2, to procuring new ballistic-missile submarines (SSBNs) that will replace Ohio-class boats, to exploring follow-on options for the Minuteman III intercontinental ballistic missile (ICBM). These seemingly divergent trends raise a number of questions: Can the United States continue to implement nuclear reductions and still deter rivals, dissuade competitors, and discourage proliferation? Should it retain the strategic triad of bombers, SSBNs and ICBMs? Must it replace its aging nuclear forces?

Proponents of deeper nuclear cuts generally advocate three distinct (but not mutually exclusive) measures: decreasing the size of the U.S. strategic nuclear arsenal through reductions in deployed and reserve warheads; divesting force structure by eliminating delivery systems; and deferring, scaling back, or abandoning planned nuclear modernization programs. Yet these arguments are problematic for several reasons.

For instance, the case for further cuts in the American arsenal reflects an outdated and potentially counterproductive emphasis on the U.S.-Russia nuclear balance. According to this perspective, because the size of the arsenal was originally driven by the need to deter a Soviet attack, and because Washington and Moscow are no longer adversaries, it should be possible to preserve strategic stability with far fewer weapons. Thus the two sides should continue to cap or reduce warhead numbers in tandem.

In the past, when the American and Soviet (and later Russian) arsenals dwarfed the arsenals of other nuclear powers by orders of magnitude, this view made sense. As Washington’s quantitative margin of advantage declines, however, some friendly nations might lose confidence in its extended-deterrence commitments (giving them an incentive to develop their own nuclear weapons), while potential competitors might build toward parity with the United States for strategic or symbolic reasons (taking advantage of a window of opportunity). Eventually, this dynamic could lead to a multipolar world with three or more nearly equal nuclear-armed nations—a potentially unstable environment where shifting coalitions could quickly upend the nuclear balance.

At the same time, arguments that the United States should reduce its nuclear force structure while preserving warhead numbers often focus on arsenal size at the expense of arsenal composition. Yet arsenal size is only one metric that can be used to judge the adequacy of U.S. nuclear forces, and it may not be the most appropriate one. Put simply, cutting force structure would make it increasingly difficult to achieve a balance between survivability, promptness, flexibility, lethality and visibility—some of the many weapons attributes that enable the United States to deter a variety of potential adversaries across a range of plausible scenarios.

Finally, by claiming that existing U.S. nuclear forces will remain adequate in the decades ahead, critics of planned modernization programs implicitly assume that the future security environment will not differ greatly from the present. Yet the conditions that have enabled the United States to make due with fewer nuclear weapons and avoid serious modernization efforts over the past two decades—including the absence of a hostile peer competitor and conventional military superiority over potential rivals—might not last indefinitely.

Ultimately, the United States still needs a nuclear arsenal that is large enough to dissuade other nations from pursuing parity, diverse enough to deter nuclear use across a wide range of contingencies, and viable long into the future. For the time being, therefore, it should avoid significant reductions in the size of its arsenal below the ceilings established in the New START Treaty, forgo substantial cuts in nuclear force structure, and implement planned nuclear modernization programs across all three legs of the triad.

Specifically, SSBNs will continue to be the most important element of the United States’ strategic nuclear deterrent. Not only are bombers at their bases and ICBMs in their silos more vulnerable to a disarming first strike, but the former cannot retaliate immediately in the event of an attack, while the latter offer comparatively limited targeting options given their high yield warheads (as well as launch trajectories that would carry them over Russian territory to targets at risk in East Asia and the Middle East). Nevertheless, the need to modernize the existing but aging undersea fleet has generated controversy, largely because of the costs associated with designing and building a replacement for the current Ohio-class SSBNs.

What critics of this program often fail to appreciate, however, is that forgoing the development of a new ballistic-missile submarine would force the United States to rely on less-stealthy alternatives, whether a modified Virginia-class attack submarine or newly-built Ohio-class SSBNs. Moreover, reducing the total number of SSBNs the United States plans to purchase could create pressure to consolidate remaining boats, which are currently divided between two bases. Yet this would also leave them bound to a single ocean. Either scenario would reduce the survivability of the undersea deterrent—its most important attribute.

By contrast, the bomber force (which includes penetrating systems like the B-2 that can release gravity bombs directly over enemy targets as well as standoff systems like the B-52 that can release cruise missiles from beyond the range of enemy air defenses) has arguably been the least important leg of the triad since the deployment of ballistic missiles in the 1960s. Nevertheless, bombers are likely to become far more relevant in the future, particularly if conventional precision-strike systems and nuclear weapons proliferate more widely.

For instance, despite their function as nuclear-delivery systems, stealthy aircraft like the B-2 and the planned long-range strike bomber (LRS-B) will have the increasingly important role of providing conventional military options in highly contested environments. In fact, this will arguably be their primary role. Because the spread of extended-range guided weapons could threaten the United States’ ability to conduct expeditionary military operations by holding forward bases and nonstealthy aircraft at risk, platforms that can operate from range and penetrate defended airspace will become more critical for conventional deterrence, crisis stability, and power-projection.

Both the penetrating and standoff components will also be tasked with providing limited nuclear options if necessary. Because the United States has no plans to build new nuclear warheads, bombers will remain the only strategic delivery systems capable of employing the only low-yield weapons that will remain in the U.S. stockpile. Importantly, these weapons might be the most credible deterrent to a limited nuclear attack by a minor nuclear power. Of course, this will also require the United States to refurbish its aging nuclear gravity bombs and replace its nuclear-armed cruise missiles before they are retired.

Lastly, the importance of ICBMs has undoubtedly declined since the end of the Cold War. Yet significant cuts to this leg of the triad could introduce a source of instability in the future. In particular, the role of ICBMs as a “missile sink” (that is, a force-in-being that maximizes the number of aim points an adversary would have to target in a first strike on U.S. nuclear forces) still has value, because no opponent can seriously degrade the U.S. ICBM force without expending a disproportionate share of its own arsenal. The United States should, therefore, continue to extend the life of its Minuteman III ICBMs, which would enable it to defer embarking on a wholesale replacement program.

In the end, there are credible reasons for the United States to forgo deep reductions in the size of its nuclear arsenal, avoid significant cuts in its nuclear force structure, and move ahead with planned nuclear modernization programs. By shrinking the arsenal and divesting force structure, Washington could find it increasingly difficult to simultaneously preserve strategic stability with a nuclear peer, deter nuclear use by hostile regional powers, and dissuade other nations from building nuclear weapons. Moreover, abandoning modernization efforts would be tantamount to major nuclear cuts given the age of existing warheads and delivery systems, the long timelines associated with developing new capabilities, and the fact that the United States no longer has the infrastructure or personnel in place to quickly begin producing nuclear weapons if necessary—a situation that will only grow worse over time.

Evan Braden Montgomery is a senior fellow atthe Center for Strategic and Budgetary Assessments (CSBA). This article draws on his newly released CSBA report, The Future of America’s Strategic Nuclear Deterrent.

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