Washington and Seoul have yet to officially comment on Thursday’s test.
On Friday, South Korean President Yoon Suk Yeol accused North Korea of “reckless provocations.”
Daniel A. Pinkston, an expert in northeastern Asian security at Troy University in Seoul, pointed out there were many technical challenges with operating an underwater unmanned vehicle, and that North Korea may be displaying its supposed capabilities across sea and air for show, rather than any real intent.
“The thing is, how do you actually use them for anything other than a deterrent? So as soon as North Korea uses a nuclear weapon, it’s suicide, right?” he told NBC News.
“The kind of rhetoric that they use is an effort to use weapons for coercion, to compel adversaries into making concessions or lifting sanctions or ending exercises.”
Ankit Panda, a senior fellow at the Carnegie Endowment for International Peace, said that footage of the launch on state TV was the world’s first glimpse of the missiles.
The weapon could be similar to Russia’s Poseidon underwater drone, but questions remain, he said on Twitter.
North Korea has been preparing the underwater drone since 2012 — the politburo of the ruling Workers’ Party of Korea was first told about it in October 2021, according to KCNA.
The country has dozens of nuclear warheads, but it’s unclear whether it has mastered the technology to fit them onto the new weapons it claims to have developed.
Lt. Gen. Scott Berrier, director of the U.S. Defense Intelligence Agency, told reporters at a briefing Wednesday that the U.S. would stay vigilant but that Kim did not appear poised to carry out a nuclear test.
Patrick Smith is a London-based editor and reporter for NBC News Digital.
Reuters and Associated Press contributed.