On March 27, North Korea also released photos of Mr. Kim inspecting Hwasan-31, a small standardized nuclear warhead kit that can be mounted on its various nuclear-capable missiles and drones.
If the module was a real thing, the photos mean that the North is showing off an ability to mass-produce standardized nuclear warheads, said Hong Min, an expert on North Korean weapons at the Korea Institute for National Unification in Seoul. Mr. Kim has also called for mass-producing nuclear warheads for an “exponential” increase in the country’s nuclear arsenal. Last month, he ordered his government to step up the production of weapons-grade nuclear materials.
South Korean officials said that some of the North’s claims, like the purported capabilities of its underwater drones and supersonic missiles, were exaggerated. The reaction in Washington and Seoul has been to vow to strengthen their alliance — made easier by the fact that Mr. Yoon takes a far more hawkish view of how to deal with the North than did his predecessor, Moon Jae-in, who visited Mr. Biden in May 2021.
So the two leaders are expected to speak at length, publicly, about “extended deterrence,” with Mr. Biden offering more regular, visible visits of nuclear-armed submarines and aircraft to South Korea, bolstering the recently reinstated and expanded joint military exercises. (The exercises were variously suspended and scaled down under Mr. Trump.)
Kim Tae-hyo, a deputy national security adviser for Mr. Yoon, said that a top agenda item at the summit was how to boost South Korean confidence in Washington’s commitment to protect its ally with its nuclear umbrella. But Korean officials say that is more dependent on their confidence in the sitting American president — and whether, in the midst of a North Korean attack on the South that employed tactical nuclear weapons, Washington would be willing to take the risk to enter nuclear combat.