If the Pyongyang regime deploys an effective undersea nuke—and all signs point toward that eventuality—it might be able to sail a sub behind U.S. defenses on the Korean Peninsula and launch a surprise strike on South Korean cities.
The new undersea threat comes at a time of escalating hostility between the United States and North Korea. The communist country recently produced a miniaturized nuclear warhead small enough to fit inside its missiles, according to The Washington Post. Warhead-miniaturization is “a key threshold on the path to becoming a full-fledged nuclear power,” the Post reported.
In response to the report, President Donald Trump vowed to to inflict “fire and fury” on North Korea. A North Korean army commander called Trump’s threat “a load of nonsense.”
On Aug. 8, Pyongyang announced it was preparing a plan for a preemptive strike on the U.S. military base on the Pacific island of Guam. Responding to that threat, U.S. Defense Secretary James Mattis warned North Korea to “cease any consideration of actions that would lead to the end of its regime and the destruction of its people.”
As the rhetoric on both sides grows more heated, North Korea is marching along the path toward a functional, long-range nuclear arsenal. Pyongyang possesses a increasing number of rockets that are presumably compatible with the new, smaller warheads it reportedly has developed. On July 4 and again on July 28, North Korea tested a ground-launched intercontinental ballistic missile capable of hitting the continental United States from the Korean Peninsula. Pyongyang also fields hundreds of shorter-range rockets.
The U.S. military has deployed missile defenses that can, in theory, intercept these ground-launched rockets. To protect South Korea and American forces in that country, the U.S. Army has positioned a Terminal High Altitude Area Defense system in central South Korea. To destroy ICBMs headed for North America, the Army has installed ground-based midcourse defense (GMD) rockets in Alaska and California.
But at present, the United States lacks an effective defense against a short-range, submarine-launched rocket targeting South Korea. THAAD’s powerful radar points north in order to detect rockets coming from North Korea, leaving most of southern South Korea open to attack from other directions. And the GMD interceptors in Alaska and California lack the range to protect South Korea.
“The missile defenses... would be ineffective against the missiles fired from the waters east, west, and south of the lower Korean Peninsula,” Michael Elleman and Michael J. Zagurek Jr., analysts at the U.S.-Korea Institute at Johns Hopkins, warned in a 2016 report.
Pyongyang is apparently eager to exploit that vulnerability. In April 2016, North Korea test-fired a rudimentary rocket from one of its small, diesel-fueled submarines.
The 2016 test was outwardly unimpressive. The submarine-launched ballistic missile, or SLBM, traveled only 18 miles. The sub itself is an older design that probably can’t reliably cross the Pacific Ocean in order to threaten the continental United States. “I certainly wouldn’t want to be on a North Korean submarine,” Eric Wertheim, an independent U.S. naval analyst and author of Combat Fleets of the World, told The Daily Beast. “They’re not the safest of underwater platforms.”
But an SLBM and its launching vessel need not be too technologically advanced to upset the balance of power on the Korean Peninsula. It need only sail a short distance from its base and lob a missile at a city that THAAD’s north-facing radar doesn’t cover. “The SLBM is good for shooting behind THAAD at targets in South Korea, so the system is useless,” Jeffrey Lewis, a nuclear expert who blogs at Arms Control Wonk, told The Daily Beast.
The obvious short-term solution is for the United States to deploy more THAAD systems to South Korea—and position them to face east, west, and south. But the installation of the first THAAD battery elicited bitter protests from South Koreans wary of military escalation on the peninsula, as well as from China, which fears THAAD’s radar could track Chinese forces.
For now, North Korea’s unsophisticated sub-launched missile could give the country a major strategic advantage—and back up its increasingly forceful threats.