North Korea tests submarine cruise missiles from its 'Frankenstein' vessel for the first time

When North Korea unveiled the Hero Kim Kun Ok submarine in September 2023, it said the vessel could launch tactical nuclear weapons from underwater. South Korea’s military assessed at the time that it did not appear capable of normal operation.

The submarine then went three years without any publicly reported weapons tests, suggesting technical difficulties that included its ability to right itself. On October 14, 2026, however, North Korea fired two types of submarine-launched strategic cruise missile from the vessel off its east coast, in the waters of DONGHAE.

The test was the Hero Kim Kun Ok’s first confirmed weapons trial at sea. North Korea said it launched two cruise missiles.

Photographs released by North Korea’s General Missile Bureau showed two separate launches. One missile rose vertically from the water through a plume of smoke, while another appeared to leave the surface at an angle.

Analysts assessed that the vertical missile came from a vertical launch tube and the angled one from a torpedo tube. Senior military officers watched the tests.

South Korea’s Joint Chiefs of Staff said it detected the launches and tracked them with various assets from before launch through their cruise and terminal phases. A US Navy high-altitude unmanned reconnaissance aircraft and a US Army reconnaissance and electronic warfare aircraft were also reported to have flown over DONGHAE on October 14.

The Korean Central News Agency said the launches assessed the readiness of North Korea’s underwater combat systems, improved the navy’s ability to carry out strategic missions and demonstrated the reliability of the country’s nuclear deterrent.

Shin Jong-woo, secretary general of the Korea Defense and Security Forum, said there appeared to have been severe problems stopping the submarine from testing its weapons systems until now. The latest launches showed, he said, that North Korea had resolved technical issues.

The Hero Kim Kun Ok is based on a Soviet-designed Romeo-class diesel submarine. Its hull was enlarged to hold 10 vertical launch tubes, a modification that gave it the nickname the Frankenstein submarine because of its unusual exterior.

Before October 14, 2026, North Korea’s underwater missile launches had all come from a 2,000-ton-class submarine with a single launch tube. Vertical launch systems can fire missiles faster and in larger salvos than torpedo tubes, potentially shortening warning times and making defensive responses harder.

South Korean analysts have suggested the missiles may have included the longer-range Hwasal-2 and shorter-range Pulhwasal-3-31 cruise missiles, though those identifications remain unconfirmed.

Moon Keun-sik, a submarine expert at Seoul’s Hanyang University, said deployment of the vessel “would pose a significant threat” to South Korea and the US. Underwater-launched missiles were “formidable weapons that we don't know when and where they would be fired”, he said.

Hong Min, a senior researcher at the Korea Institute for National Unification, said the submarine still has “limited operational capability”. Submerged launches, long patrols and SLBM operations have yet to be demonstrated, he said.

The tests came as North Korea steps up weapons demonstrations in what appears to be an effort to press the United States for greater concessions in any return to diplomacy. The country is also accelerating operational deployment of 5,000-ton-class destroyers, unmanned underwater vehicles and submarine capabilities as part of a wider military modernisation effort.