The United States has gone to great lengths to defend Israel and Ukraine against air and missile attacks. On October 13, the Department of Defense announced plans to equip Israel with a Terminal High-Altitude Area Defense (THAAD) Battery to protect against future Iranian missile strikes. President Biden also provided Ukraine with extensive air and missile defenses over the past two years to protect it from Russian attacks. Likewise, a U.S.-orchestrated coalition helped Israel defend itself against air and missile barrages from Iran—likely averting an escalatory response that could have led to a broader Middle East conflict. Yet why is it that the United States comes up short when it comes to defending its homeland against long-range missile threats?

This finding was the conclusion of the independent, bipartisan Strategic Posture Commission appointed by Congress. According to its October 2023 report, “the currently-planned U.S. homeland air and missile defense capability does not adequately defend against coercive attacks from China and Russia.” The concern is not over a large-scale nuclear missile attack (the United States relies on its nuclear forces to deter such threats) but, rather, limited attacks with the intent to “deter the United States from defending or supporting its allies and partners in a regional conflict.” 

The commission also supports the long-standing policy of staying ahead of the growing North Korean intercontinental-range missile threat. Still, it warns, as do other senior military commanders, that the United States is at risk of falling behind without further improvements to its homeland defenses.

Referring to Israel’s Iron Dome missile defense system, which the U.S. helped develop, former President Donald Trump has made homeland defense a recurring theme in his campaign, arguing for a “state-of-the-art” missile defense system to protect the United States. It is unlikely these references to building an “Iron Dome” for the United States are about creating an impenetrable shield against large-scale missile attacks. Rather, it likely points to a need for defenses that can counter limited attacks that would be designed to coerce us, degrade our military capabilities, and damage civilian infrastructure. While this would seem to be a high-risk step for any adversary to take, Moscow or Beijing may see such attacks as worth the risk, especially if the intended high-value targets are not adequately defended—or not defended at all.

We do not know Vice President Kamala Harris’ views on the matter. However, if a prospective Harris administration merely affirms the five-year funding plan for homeland defense activities in the Missile Defense Agency (MDA)’s budget proposed by President Biden, then it will be impossible for the United States to pace the missile threats identified by the Strategic Posture Commission and U.S. intelligence agencies. It is not a good sign that the Fiscal Year 2025 budget request for homeland missile defense declined to $2.7 billion from $3.3 billion in the previous year.

Today, the role of homeland defense is to protect against North Korea’s long-range missiles; there is inadequate protection provided against even limited Russian and Chinese ballistic or cruise missiles. Currently, there are forty-four ground-based interceptors fielded, with another twenty newer systems planned for by 2030. This posture may have been sufficient in the past to cope with the threat to the homeland. Still, it is inadequate for the task in the coming years—which is disturbing given that the number one priority of Republican and Democratic defense strategies has been to “defend the homeland.”

How Did We Get Here?

The development and deployment of homeland missile defense have been stymied by a long-standing policy debate prompted by those who believe missile defenses will start an action-reaction arms race with Russia and China. The alternative view—adopted by the authors—is that even less-than-perfect defenses contribute to the deterrence of adversaries and assurance of allies by lessening the vulnerability of the United States to coercive missile threats. The upshot of this ambivalence on missile defense is that successive U.S. administrations have intentionally designed homeland defenses—in numbers, technology, and performance—to stop short of providing the capability to defend against Russian and Chinese missile forces, even against small attacks.

This ambivalence vis-a-vis Russia and China has restricted the pursuit of new systems, platforms, and technologies to cope with rapidly advancing offensive threats. It has even prevented the use of other militarily effective missile defense systems to complement the GBIs to provide a layered defense against North Korean missiles. For example, in November 2020, a U.S. Navy ship successfully intercepted a mock North Korean intercontinental-range missile with the Standard Missile 3 (SM-3) interceptor. Yet, integrating the SM-3 missile (which was designed principally for regional defense) into our homeland defense posture has been blocked for fear of potential Russian and Chinese objections. 

Critics have reinforced their opposition to any expansion of homeland defense by building the strawman argument that the United States must have leak-proof defenses for missile defense investments to be worth the cost. However, the objective is not to replace deterrence with an impenetrable defense; rather, it is to reinforce the threat of retaliation by thwarting the missile attack in the first place. In this way, an adversary must worry not only about the likely success of his attack but also about the prospect of U.S. retaliation. Far from replacing deterrence, defenses enhance deterrence.

Finally, among detractors of missile defense, there is a failure to appreciate that the increasing vulnerability of the U.S. homeland to even limited missile attacks makes our allies nervous—a problem common to the Cold War. They are starting to wonder whether the United States would be willing to run nuclear risks to defend them in the face of this vulnerability. Providing a measure of protection for the homeland helps reassure allies that Washington will be there when the going gets tough—so they do not have to acquire nuclear arsenals of their own.

A New Missile Defense Strategy

If the United States is to confront the growing danger of conflicts involving multiple adversaries armed with nuclear and non-nuclear missiles, the next president ought to be prepared to change America’s missile defense strategy.

Most importantly, consideration should be given to an approach that leverages a mix of defensive systems in a “layered” defense. The different layers would comprise various interceptors capable of destroying attacking missiles and warheads during different phases of flight, from launch through the midcourse in outer space and then during the terminal reentry phase. This approach provides more opportunities to destroy enemy missile launches, especially compared to the current posture that relies exclusively on a single layer of ground-based interceptors. Interceptors at each layer “thin the herd” for the following layers. Attacking warheads containing countermeasures that may fool the defense in one layer may prove useless in another. In terms of enhancing deterrence and limiting damage from such attacks, multiple layers add uncertainty and risk to the attacker’s calculation while reducing the technical requirements for any given interceptor because it does not have to work perfectly.

A strategy tailored around this objective introduces a wider range of defense concepts, technologies, and systems that can operate across all domains to thwart missile attacks on the homeland. There are two reinforcing paths to this end. The first approach is to pursue a series of quick fixes implemented over the next several years to begin closing the gap in our defense opened by the expansion of North Korea’s long-range missiles. The second is to identify follow-on measures to lay a foundation for a longer-term shift in our military strategy and posture to cope with the more advanced missiles North Korea and Iran have under development while simultaneously undermining Russia’s and China’s ability to hold the United States, hostage, by threatening to escalate to limited ballistic and cruise missile strikes in a crisis or conflict.

Quick Fixes

Several modest steps can be taken now to ensure that the nation’s current homeland defenses, known as the Ground-based Midcourse Defense system, do not fall further behind the rogue state missile threat. 

First, the Department of Defense should take measures to ensure it preserves its inventory of forty-four ground-based interceptors (GBI) well into the 2030s. The current inventory can be improved against North Korean ICBMs if all forty-four GBI Kill Vehicles are upgraded with the latest software and hardware configurations that are presently on only one-third of the interceptors.

Second, the Pentagon should reassess the requirement for an additional interceptor site in the eastern part of the United States. Such a site provides valuable added “battlespace,” beyond the sites in Alaska and California, which equates to more shot opportunities for North Korean missiles and potential Iranian missile launches against the eastern part of the United States.

Third, the United States can potentially upgrade the Navy’s sea-based SM-3 IIA interceptor to shoot down intercontinental-range missiles. The SM-3 can be based on ships or on land to serve as an “underlayer” to the GMD system, providing dozens of additional interceptors over the next few years to augment the protection of the homeland. As noted earlier, in 2020, the Department of Defense (DoD) successfully tested a modified SM-3 IIA, demonstrating the feasibility of destroying an Intercontinental Ballistic Missile (ICBM) warhead.