North Korea Fires Pulhwasal-3-31 Cruise Missiles From a Submarine for the First Time Since 2024

North Korea has test-fired two types of strategic cruise missiles from underwater off its east coast, one of them identified as the Pulhwasal-3-31, in the country’s first publicly disclosed submarine-launched cruise missile test since January 2024. State news agency KCNA reported on October 15 that the launches had taken place in the East Sea the previous day under the supervision of senior officials, with Kim Jong Un notably absent. The agency stated that the test aimed to examine “the current mobilized posture of the underwater combat systems,” but did not name the launch platform or disclose how far either missile flew. The test highlights how far Pyongyang has moved towards giving its navy a share of the nuclear strike role, which for decades rested almost entirely on land-based ballistic missiles.

South Korea’s Joint Chiefs of Staff stated on October 15 that it had tracked the missiles from before launch until the end of their flight, while declining to name the surveillance assets involved, citing confidentiality arrangements with the United States. Its spokesman, Captain Jang Do Young, reported that one missile had been fired from a vertical launching system and the other from a torpedo tube, details KCNA itself did not provide. That combination points to a boat carrying purpose-built missile tubes alongside its torpedo armament, and experts quoted by the Korea Times identified the likely platform as the 3,000-ton class submarine Hero Kim Kun Ok. The launch followed a ballistic missile test on October 3 and the firing of multiple ballistic missiles towards the East Sea on October 12, with KCNA also claiming that the Pulhwasal-3-31 had been fired from land the previous week.

The Hero Kim Kun Ok was launched at Sinpo on September 6, 2023, as what Pyongyang called its first tactical nuclear attack submarine, with Kim Jong Un stating at the ceremony that arming the navy with nuclear weapons “brooks no further delay.” The boat is widely assessed to be a heavily modified Soviet-designed Romeo class hull, and North Korea is still not believed to have a modern missile submarine in full operation. Kim nevertheless toured an 8,700-ton nuclear-powered missile submarine under construction in late 2025, and has described the U.S.-South Korean nuclear submarine deal as a threat to stability on the peninsula. The program remains considerably behind those of the North’s neighbours, with Japan having launched its seventh Taigei class boat and France firing ballistic missiles from dedicated nuclear-powered submarines.

The Pulhwasal-3-31 was first tested on January 24, 2024, and four days later two were fired from the older 2,000-ton class submarine 8.24 Yongung, with KCNA claiming that they flew for 7,421 and 7,445 seconds before striking an island target. The designation has been widely linked by analysts to the Hwasan-31 tactical nuclear warhead unveiled in 2023. Cruise missiles flying at low altitude are significantly harder for ground-based radars to detect than ballistic missiles, the same quality that has driven Pakistan’s work on its extended-range Fatah-4 design. KCNA has not disclosed the designation of the second missile tested on October 14, and none of its flight time claims for the 2024 tests have been independently verified.