North Korea continued its inexorable march toward a more robust, diversified nuclear-capable missile force by successfully testing a solid-fueled ICBM. The new missile augments North Korea’s military threat to the United States since it can be launched more quickly than the regime’s existing liquid-fueled ICBMs. This makes it harder to detect and target.

But Pyongyang is up to even more. It is concurrently developing a new generation of tactical nuclear weapons and missile systems to further threaten America’s allies.

On April 13, North Korea conducted the inaugural launch of the three-stage Hwasong-18 solid-fuel ICBM. It flew 1,000 kilometers on a lofted trajectory so as to not fly over Japan. The Hwasong-18’s full range is not known, but previous North Korean ICBMs were assessed as able to target the entire continental United States with nuclear weapons. North Korean leader Kim Jong-un declared the Hwasong-18 would “greatly reinforce” the country’s strategic deterrent, enhancing both its nuclear counterattack posture and its offensive nuclear strategy.

Liquid propellant, used in the existing Hwasong-15 and Hwasong-17 ICBMS, is highly corrosive and cannot be maintained in a missile. Instead, it can only be loaded after deployment to the field and shortly before launch. The fueling itself is a lengthy, hours-long process.

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By contrast, the Hwasong-18’s solid fuel is loaded during manufacture, leaving the missile able to launch quickly. This shortens the time the missile is exposed and vulnerable to detection and targeting by allied forces.

A solid-fueled missile does not require fuel and oxidizer trucks, which further reduces its observable signature to overhead satellites. It is also less delicate than a liquid-fueled missile, enabling it to be transported on its mobile launcher across a broader range of terrain.

North Korea first revealed the Hwasong-18—along with 12 liquid-fueled multi-warhead Hwasong-17 ICBMs—at its February 2023 military parade. Pyongyang likely tested the first stage of the Hwasong-18 in December 2022, announcing it had a thrust of 140 tons of force, which is greater than any U.S., Russian, or Chinese ICBM.

In January 2021, Kim Jong-un directed the development of a solid-fueled ICBM as part of an ambitious five-year plan of nuclear weapons and missile delivery systems. Other tasks assigned at the time were: developing smaller, tactical nuclear warheads; producing large nuclear warheads; improving the accuracy range of ICBMSs to 15,000 km; creating hypersonic gliding flight warheads; and developing a nuclear-powered submarine capable of launching nuclear strategic weapon under water.

Two years later, Kim directed development of an “ICBM system whose main mission is quick nuclear counterstrike.” This likely was a reference to the Hwasong-18.

The Hwasong-18 is the latest in a long list of new missiles of all ranges developed by North Korea during Kim Jong-un’s reign. The regime is producing a new generation of advanced missiles that are more accurate, more mobile, and more difficult to detect and target, with some having an enhanced ability to evade allied missile defenses.

In 2022, Pyongyang cumulatively launched a record-high 69 ballistic and six long-range cruise missiles. Some of the launches included salvo launches of multiple missiles simulating nuclear attacks on South Korean ports, airfields, and hardened military command targets. The regime has launched missiles from road-mobile transporters, railcars, submarines, and an underwater launch from a lake.

Pyongyang is attempting to gain tacit acceptance of its violations of UN resolutions (and, hence, prevent additional sanctions) through routinization of its missile launches and reliance on Chinese and Russian obstructionism at the UN Security Council. By depicting its military provocations as justified responses to the resumption of U.S. and South Korean military exercises, Pyongyang seeks to coerce the allies to curtail future drills.

Kim vowed North Korea would “exponentially increase” nuclear weapon production in 2023 to counter perceived threats from the U.S. and South Korea. Pyongyang has recently emphasized production of smaller tactical nuclear warheads for battlefield use. The regime is on its way to developing capabilities that go beyond deterrence to a viable offensive warfighting strategy.

In a few years, North Korea could have 100–200 nuclear warheads, dozens of mobile ICBMs, and hundreds of improved, survivable short-range, medium-range, and intermediate-range missiles as well as submarine-launched missiles.

Last September, North Korea approved a new nuclear doctrine which lowered the threshold for its use of nuclear weapons. Pyongyang declared it would initiate a nuclear strike in response to, or preemptively if it perceived, allied preparations for conventional or nuclear attacks on regime leadership, nuclear command structure, or important strategic targets.

A more survivable North Korean nuclear force could create first-strike uncertainty for the United States as to whether it is able to target all of North Korea’s nuclear weapons. Greater North Korean nuclear capabilities could undermine the effectiveness of existing allied military plans.

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The regime could feel emboldened to use nuclear threats to coerce Seoul into accepting regime demands and deter the United States from responding. Pyongyang might also assume that conditions for military action had become favorable if it believed the U.S. extended deterrence guarantee had been undermined.

As long as Pyongyang rejects all attempts by the U.S., South Korea, and Japan at resuming diplomatic dialogue, Washington and its allies must enhance their individual and collective missile defenses against the escalating North Korean threat. In 2022, the three countries resumed trilateral ballistic missile defense exercises after a four-year hiatus. Last November, the three leaders agreed to “share North Korean missile warning data in real time to improve each country’s ability to detect and assess the threat posed by incoming missiles.”

Missile defenses are most effective when systems are incorporated into a seamless and cohesive network. Linking South Korean, American, and Japanese sensors would enable more accurate interceptions by tracking attacking missiles from multiple angles and multiple points throughout the flight trajectory.

To date, South Korea has refused to integrate its Korea Air and Missile Defense system into the more comprehensive allied system due to lingering animosities arising from Japan’s 1910-45 occupation of the Korean Peninsula. However, President Yoon Suk Yeol’s recent bold move to mend relations with Japan has laid the foundation for enhanced military cooperation. Tokyo responded by lifting trade restrictions and resumed bilateral meetings of economic, business, and military cooperation.

President Joe Biden should raise the issue during Yoon’s forthcoming visit to Washington, as well as during a trilateral summit with Prime Minister Fumio Kishida in May.