North Korea showcasing 'second-strike capability' with submarine reveal, expert says

North Korea revealed the exterior of an 8,700-ton nuclear-powered submarine currently under construction for the first time on Thursday.

An 8,700-ton nuclear-powered strategic guided missile submarine is seen during an inspection by North Korean leader Kim Jong-un, not pictured, in this photo provided by the state-run Korean Central News Agency on Dec. 25. [KOREAN CENTRAL NEWS AGENCY]

North Korea revealed the exterior of an 8,700-ton nuclear-powered submarine currently under construction for the first time on Thursday.

The move is widely seen as an attempt to highlight progress on one of the five core tasks for defense capability development outlined by leader Kim Jong-un at the Eighth Congress of the Workers’ Party of Korea in 2021 — the development of nuclear-powered submarines and underwater-launched nuclear strategic weapons — while underscoring Pyongyang’s claim that it is an irreversible nuclear-armed state equipped with underwater nuclear strike capabilities.

The disclosure also appears intended as a pre-emptive warning against the U.S. decision to assist South Korea's pursuit of nuclear-powered submarines.

The North’s Korean Central News Agency (KCNA) reported Thursday that Kim provided on-site guidance for the construction of what it called a “nuclear-powered strategic guided missile submarine.” The state-run media said the submarine displaces 8,700 tons but did not elaborate on specific stages of construction.

North Korean leader Kim Jong-un inspects the building site for a 8,700-ton nuclear-powered strategic guided missile submarine in this photo released by the Korean Central News Agency on Dec. 25. [KOREAN CENTRAL NEWS AGENCY]

Why reveal the full exterior now?

Experts say the decision to release images showing the submarine’s complete external form may be intended to signal that development has entered its final stages.

“Judging by standard construction phases, it appears that core modules for a nuclear submarine — including the reactor and missile launch structures — have already been installed inside the hull,” said Hong Min, a senior research fellow at the Korea Institute for National Unification.

“Showing it to the supreme leader suggests the vessel has reached a stage where the full silhouette is complete, meaning the reactor installation is finished,” he said. The modules include key propulsion components such as the reactor, turbine and cooling systems.

“South Korea and the United States are closely monitoring North Korea’s weapons development,” said South Korea’s Joint Chiefs of Staff on Thursday, adding that they are “analyzing the disclosure along with other intelligence.” The statement suggests that authorities are examining the possibility that a nuclear reactor may already have been transferred to North Korea.

This photo, carried by North Korea's official Korean Central News Agency on Dec. 13, 2025, shows leader Kim Jong-un attending a welcoming ceremony the previous day for North Korean military engineer troops who returned home after being deployed to Russia's Kursk region to remove landmines amid the Russia-Ukraine war. [YONHAP]

In September, South Korean military officials warned that deepening military cooperation between Russia and North Korea could potentially lead to “the transfer of reactor technology” for nuclear-powered submarines, saying “related developments were being closely watched.”

Still, South Korean intelligence has been cautious in its assessments, saying that there is no concrete evidence that a Russian nuclear module has been handed over to Pyongyang.

“What North Korea reveals and what it actually deploys operationally are two different things,” said Park Won-gon, a professor of North Korean studies at Ewha Womans University. “Even if Pyongyang received small reactor technology from Russia, it would still take considerable time to realize the technology, and the likelihood that it would function properly remains low.”

Yang Uk, a research fellow at the Asan Institute for Policy Studies, noted that missile-related structures appear to occupy about half the hull. “That raises the possibility that the lead vessel could even adopt a diesel-electric propulsion system,” Yang said.

North Korean leader Kim Jong-un, center, tours a weapons facility with his daughter, Kim Ju-ae, right of center, in this photo released by the Korean Central News Agency on Dec. 24. [KOREAN CENTRAL NEWS AGENCY]

Warning of “merciless retaliatory strikes”

Kim also reaffirmed his commitment to strengthening North Korea’s existing nuclear forces. “It is needed to make the enemy understand with no doubt that they will be surely forced to pay a dear price when they violate the security of the DPRK's strategic sovereignty and that they will face a merciless retaliatory attack if they try to select a military option,” said Kim, according to the KCNA. DPRK refers to North Korea's official name, the Democratic People's Republic of Korea.

He added that “further strengthening the nuclear shield — the absolute guarantee of security — and solidifying its irreversible status is the sacred mission and duty of our generation.”

“It reflects highly calculated political and military intentions,” said Lim Eul-chul, a professor at Kyungnam University’s Institute for Far Eastern Studies, pointing out that the move goes beyond a simple show of force. “Pyongyang is showcasing a ‘second-strike capability’ — the ability to retaliate from underwater even if land-based nuclear facilities are destroyed.

North Korean leader Kim Jong-un and his daughter Ju-ae attend the 80th anniversary of the establishment of the Air Force of the Korean People's Army at the Kalma Airport of the 59th Kil Yong Jo Hero Regiment of the 2nd Air Division on Nov. 28. [KOREAN CENTRAL NEWS AGENCY]

“North Korea’s strategic nuclear submarines carry significant implications,” said conservative People Power Party Rep. Yu Yong-weon. “Submarine-launched ballistic missiles (SLBMs) are difficult to detect and could enable nuclear retaliation against the U.S. mainland.

North Korea described the vessel unveiled Thursday as a “nuclear-powered strategic guided missile submarine,” claiming it can carry “guided missiles.” The term “nuclear-powered” refers to nuclear propulsion, while “strategic guided missiles” implies ballistic missiles capable of carrying nuclear warheads — suggesting Pyongyang is claiming to be building a nuclear-armed, nuclear-powered ballistic missile submarine.

South Korea, by contrast, is pursuing nuclear-powered submarines that do not carry nuclear weapons, known as attack submarines.

Based on the released images, the Korea Defense and Security Forum (Kodef) assessed that the submarine could carry up to 10 SLBMs and identified six horizontal torpedo launch tubes in the bow. Kodef added that what appear to be new heavyweight torpedoes designed to reduce radiated noise, along with underwater weapon systems believed to be sea mines, were also visible.

North Korean leader Kim Jong-un, center, is seen observing the launch of a new surface-to-air missile on Dec. 24. [KOREAN CENTRAL NEWS AGENCY]

A warning shot over South Korea’s plans

Kim also addressed South Korea’s pursuit of nuclear-powered submarines, which he claimed that Washington had "agreed on at the solicitation of Seoul recently.” He said North Korea “regards it as an offensive act severely violating its security and maritime sovereignty and a threat to its security that must be countered.”

Analysts say the remarks are intended to frame the situation as a “nuclear submarine standoff,” shifting responsibility for rising tensions on the Korean Peninsula onto Seoul and Washington while justifying Pyongyang’s nuclear advancement and naval nuclear armament.

Kim’s assertion that the North’s ruling party “will stay definitely unchanged in their national security policy and their principle of deterring the enemy” aligns with that narrative.

North Korean leader Kim Jong-un, right, attends the completion ceremony of a hotel at the Samjiyon tourist zone near Mount Paektu, accompanied by his daughter Kim Ju-ae, on Dec. 23. [RODONG SINMUN]

A spokesperson for the North’s Defense Ministry reiterated Kim's stance in a statement carried by the KCNA. The ministry condemned the U.S. Navy’s nuclear-powered attack submarine USS Greeneville, a 6,900-ton vessel, for docking at a naval base in Busan on Tuesday, accusing Washington of trying “to permanently introduce grave nuclear instability into the security environment" of the DPRK.”

“The [submarine reveal] amounts to another declaration that denuclearization talks are over,” said Prof. Lim. “Instead, North Korea may try to leverage its underwater strike capabilities targeting the U.S. mainland to demand nuclear arms reduction negotiations.”

The KCNA did not disclose the time or location of Kim’s on-site inspection, but it is widely believed to have taken place at the Sinpo South Shipyard in South Hamgyong Province. Observers note that in a photo carried by the Rodong Sinmun, the official newspaper of North Korea's ruling party, Kim’s daughter, Kim Ju-ae, was seen wearing the same outfit as at the opening ceremony of a local factory in Sinpo last Friday, lending weight to that assessment.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom. BY CHUNG YEONG-GYO, YOON JI-WON, SHIM SEOK-YONG [kim.minyoung5@joongang.co.kr]