In 2005, an anticipated missile threat to the homeland prompted the expeditious fielding of a missile defense capability to defend the United States. Today, that threat is real, expanding, and most likely nuclear. Our defense needs to also be real and effective for today and into the future.

A recent report by the think tank Rand estimates North Korea has 50 nuclear weapons in its arsenal and, by 2027, will have in excess of 200 and several dozen intercontinental ballistic missiles to complement its several hundred theater ballistic missiles. The director of national intelligence’s 2021 Annual Threat Assessment clearly states: “North Korea will be a [weapons of mass destruction] threat for the foreseeable future, [and] the country is actively engaged in ballistic missile research and development.”

While we must not cast diplomacy aside, we should recognize deterrence is an essential element in any strategy for dealing with the North Korean nuclear missile threat. Deterrence matters, and Adm. Charles Richard, commander of U.S. Strategic Command, framed the point well when he said: “A robust and credible layered missile defense system paired with our conventional and nuclear force capabilities provide the ability to deter strategic attacks, deny benefits, and impose costs against any potential adversary.”

Deterrence discourages an adversary by instilling doubt and anxiety in their decision calculus. Our Ballistic Missile Defense System “denies benefit” by planting that seed of doubt in North Korea’s decision calculus; the doubt that an attack on the United States will succeed.

Today, our defense rests on the Ground-based Midcourse Defense system, or GMD, and its 44 interceptors. But that alone is not going to be adequate to deal with the threats of 2027. Defending our homeland is vital. Looking to the next decade, we need to stay ahead of our threats. Our concerns are four-fold: technology, numbers, layers and sensors.

Technology: Advancing the effectiveness of our missile defense capabilities is extremely important. The Missile Defense Agency recently awarded two contracts, to two teams, to competitively develop a Next Generation Interceptor, or NGI, to overcome the shortcomings in the current interceptor fleet and provide a path to outpace future threats. This competitive development cycle will add up to 20 new interceptors to the inventory. As long as the program enjoys support and an adequate budget from the Department of Defense and Congress, we are on solid ground for the technology.

Numbers: A point of concern, though, is the math: 20 new intercepts plus the current 44 will give us 64. If Rand is anywhere close, we could be outnumbered by the end of the decade. More important, we certainly cannot accept a 1-to-1 exchange ratio when we are dealing with nuclear missiles coming toward the homeland.

Layers: No single defensive system is successful 100 percent of the time, and we cannot base the defense of America solely on the hope of success for every GMD intercept. We need the opportunity for a second engagement in the event GMD’s interceptors do not destroy the in-bound threat. Developing a layered defense is a vital strategy for our nation. We have the technology. MDA recently demonstrated the SM-3 Block 2A missile could intercept an ICBM. All we need now is an aggressive plan to truly build our layered approach for homeland missile defense.

Sensors: Lastly, our future missile defense architecture needs to have the right capabilities to “see the threat” and enable successful defenses. As Gen. John Hyten, vice chairman of the Joint Chiefs of Staff, has stated: “If you can’t see it, you can’t shoot it. And if you can’t see it, you can’t deter it either.” Today’s sensor suite — a handful of terrestrial sensors — needs to advance to the next generation: space-based sensors. Our defenses need to be able to pick out the lethal objects in a cluster of countermeasures. Further, our sensors need to provide “fire control quality” information to the defensive interceptors. While a space-based sensor architecture will be expensive, it will cost far less — in both dollars and operational risk — than relying solely on a terrestrial network.

We cannot take our foot off the pedal. While it will likely take six to seven years to field our NGI, rest assured our adversaries are not standing still. The threat is real: in North Korea today, and potentially Iran tomorrow.

NGI funding and robust competition within the program to limit technical risk and accelerate deployment are essential to stay on plan. The DoD needs to initiate a real commitment to developing the homeland’s layered defense and creating a robust, space-based missile defense sensor architecture. Development of an Aegis- and Terminal High Altitude Area Defense-based homeland defense architecture, which could be rapidly fielded, would provide the homeland an initial layered defense. Development of a space-based, discriminating sensor would enhance GMD’s and an underlayer’s performance, as well as contribute to improved theater missile defense operations.

With the upcoming debates on budget, there are sure to be opponents who will challenge the investment in our missile defenses. The issue is not how much the defense costs; the question is how much risk are you willing to buy as nuclear weapons fly toward America.

Deterrence is clearly the best approach. America needs a robust and credible layered missile defense system to deter and, if necessary, defeat a North Korean missile attack on our homeland.

Retired U.S. Air Force Maj. Gen. Punch Moulton served as the director for operations at U.S. European Command. He currently leads the Missile Defense Agency’s biannual missile defense war game. He is also the vice president for defense support and cyber strategies at Stellar Solutions. Retired U.S. Army Maj. Gen. Francis Mahon served as the director for strategy, policy and plans at North American Aerospace Defense Command and U.S. Northern Command. He also worked as the director for testing at the Missile Defense Agency. He is currently an independent aerospace defense contractor and an advisor for Stellar Solutions.