North Korea’s New “Unmanned Underwater Nuclear Attack Craft”: Red October or White Elephant?
On March 24, North Korea unveiled the “Haeil,” its first-ever nuclear-armed unmanned underwater vehicle (UUV). The data released by the North are insufficient to substantiate the Haeil’s existence, its claimed development timeline and test activities, or its claimed performance. But development of a nuclear-armed UUV is within North Korea’s technical capabilities.
Based on what has been gleaned so far about the Haeil, it would still be substantially inferior to North Korea’s nuclear-armed ballistic and cruise missiles in terms of time-to-target, accuracy and lethality. Its range limits it to coastal targets in South Korea and southeast Japan. Although this means it would not be subject to allied air and missile defenses, it would still be vulnerable to engagement by anti-submarine warfare (ASW) assets. North Korea claimed this weapon could attack “naval striker groups,” but it is too slow to pose a viable threat to ships that are underway and thus probably limited to attacking ports and known anchorages. Its slow speed, forcing it to face many hours of potential ASW detection risk before reaching target, makes it an unlikely first-strike weapon, although it would be suitable as a retaliatory weapon. Even then, most of the damage from a North Korean retaliatory strike would already have been done by missiles long before any Haeils arrived. Pyongyang might also see the Haeil as a “dead hand” option to ensure some sort of nuclear retaliation after an allied disarming strike or a lost war, but success would be far from assured, given allied ASW capabilities.
As is often the case with North Korea, the UUV would appear to have much more political than military utility. Unveiling the Haeil is consistent with the past several years of North Korean force development and related public diplomacy, messaging that:
- North Korea has large and diverse nuclear delivery capabilities;
- Allied attempts at preemption, decapitation and missile defense will, therefore, be unsuccessful, and North Korean nuclear retaliation cannot be avoided, especially against South Korea; and
- North Korea is highly technologically capable and can build the same kinds of weapons the major powers can.
All in all, the Haeil UUV brings little to the table in terms of military capabilities. Even its political value may have already been exhausted in its unveiling. Given these realities, it remains to be seen how much Pyongyang will really invest in deploying this weapons system.
Information to Date
On March 24, North Korea announced the existence of a new “underwater nuclear strategic attack weapon system,” the “Unmanned Underwater Nuclear Attack Craft ‘Haeil’.” Its mission reportedly is to “stealthily infiltrate into operational waters and make a super-scale radioactive tsunami through underwater explosion to destroy naval striker groups and major operational ports of the enemy,” and it “can be deployed at any coast and port or towed by a surface ship for operation.” According to North Korean state media reporting, the Haeil (Korean for volcano) has been under development since 2012; has “undergone more than 50 shakedowns for the past two years,” including 29 “weapon tests” that were “personally guided” by Kim Jong Un; and “its operational deployment was decided at the 6th Plenary Meeting of the 8th Central Committee” of the Workers’ Party of Korea (WPK) in January 2023.
Coverage of the launch also reported a drill in which the Haeil was “deployed” on March 21 and “reached the target point…set as a mock enemy port with its test warhead detonating underwater” on March 23, “after cruising along an oval and pattern-8 course at an underwater depth of 80 to 150 meters in the East Sea of Korea for 59 hours and 12 minutes.” That drill reportedly “verified its reliability and safety and fully confirmed its lethal strike capability.” Associated photographs showed Kim Jong Un sitting near the nose of a torpedo-like object, a surface photo of a cylinder-like object vaguely visible underwater and apparently in motion, and the plume from an underwater explosion.
On March 28, the North reported that another test of what it called the “Haeil-1” had occurred between March 25 and 27. “After cruising along a jagged and oval course simulating the distance of the 600 kilometers in the East Sea of Korea for 41 hours and 27 minutes,” the Haeil “correctly set off the test warhead underwater.” Two more photos were released with a surface image with a portion of a partially submerged torpedo-like object in motion and the plume from an underwater explosion.
Finally, on the same day, Pyongyang reported a March 27 meeting in which Kim Jong Un “guided the work for mounting nuclear warheads on ballistic missiles.” The report referred to “new tactical nuclear weapons” and their “interchangeability with different weapons systems.” Most importantly, the associated photos depicted what apparently were at least 10 units of an integrated “tactical” nuclear weapon. They also showed a graphic hanging on a wall of the inspection area with cutaway drawings of the front sections of eight different delivery systems, including the Haeil, each apparently showing the same type of warhead mounted inside.
Is It Real?
These reports and photographs are the first open-source indication of a nuclear UUV but are insufficient to substantiate the Haeil’s existence, its claimed development timeline and test activities, or its claimed performance. Kim Jong Un’s January 2021 report to the Eighth Party Congress noted a task to possess “an underwater-launch nuclear strategic weapon which will be of great importance in raising the long-range nuclear striking capability,” but the report did not specifically reference a UUV and that task was mentioned in the context of “solid-fuel engine-propelled inter-continental underwater and ground ballistic rockets” and a “nuclear-powered submarine.” The March 24, 2023 announcement noted that the Haeil was “informally reported” to the Central Committee Political Bureau at the “Defence Development Exhibition Self-Defence-2021” held in October 2021, but such a UUV was not seen in the extensive images released by North Korea at the time.
The South Korean Joint Chiefs of Staff (JCS) released a statement on March 27 saying that “there have been signs that North Korea has been developing unmanned submarines, but we assess that they are still at an elementary level.”[1] And as one analyst noted, it is indeed correct that we “can’t rule out the possibility that this is an attempt at deception.” But development of a nuclear-armed UUV is within North Korea’s technical capabilities. For example, the US and USSR developed nuclear-armed torpedoes in the 1950s. And acquiring another type of nuclear delivery system (“based on a new operational concept,” in the words of the North’s March 24 announcement) would be consistent with North Korea’s emphasis over the past few years on a diverse nuclear force resistant to preemption and decapitation, and on demonstrating its technological prowess.
Potential Capabilities
The Haeil’s configuration is uncertain. Open-source analysts thus far have assessed a diameter of some 500-800 mm (a standard 21-inch torpedo is 533 mm in diameter), and the full length of the UUV has not been displayed. The March 24 announcement’s reference to the Haeil being “deployed at any coast and port or towed by a surface ship” may suggest that it is too long and/or too large in diameter for a standard torpedo tube. (North Korea’s CHT-02D 533-mm torpedo is 7.35 meters long.)
Range and speed. Pyongyang has not described the Haeil’s propulsion type, but it almost certainly relies on batteries. The North claimed a 600-km range and 41.5-hour endurance (thus, a 7.8-knot average cruising speed) for the March 25-27 Haeil test. The 59-hour endurance claimed for the March 21-23 test may reflect a lower average cruising speed, given the likely tradeoff between speed and endurance in a battery-powered UUV, but may suggest the vehicle is capable of a somewhat longer range. These performance claims appear credible given the 500-km range (without payload), 110-hour endurance, and 2.5-knot cruising speed of the US battery-powered REMUS 620 UUV, which can sprint for brief periods at eight knots. The US system, at 324 mm in diameter and 4.8 m long, is probably much smaller than the Haeil but presumably is more technologically advanced.
A 600-km range would permit strikes against South Korea’s coastlines from a wide variety of North Korean coastal locations. The UUV would need to be launched from the southern part of North Korea’s east coast to strike targets in Japan (the southeast part of the Home Islands). Additional targeting flexibility could be gained from launching the Haeil at sea, but any towing or launch platform would be severely vulnerable even just a few hundred kilometers off North Korea’s coasts. Thus, the UUV is almost certainly a theater weapon constrained to coastal targets.
Accuracy. We do not know how the Haeil is guided or how accurate it is. To minimize its vulnerability to detection and jamming while submerged, it probably uses an inertial guidance system. The accuracy of naval inertial systems degrades over time, as much as some 1.85 km per 24 hours.[2] Ideally, the inertial system would be updated by exposing an antenna periodically (or at least once, a few hours before reaching target) to receive shore-based or satellite navigational signals, but this may increase the UUV’s vulnerability to detection while doing so, and such signals are subject to jamming and the destruction of their land-based facilities.
Lethality. The North Korean schematic showing the newly-unveiled “tactical” nuclear warhead incorporated inside the Haeil is consistent with the size of the warhead shown in the March 28 photos and the assessed diameter of the UUV. The Institute for Science and International Security has assessed that warhead as “feasible for North Korea’s experience and number of underground tests” and its yield “is likely in the range of 10 kilotons” (kt). Contrary to Pyongyang’s claims, a warhead of this yield detonated underwater (or even a very much larger one) would not produce a “tsunami.” Instead, a 10-kt warhead would throw up and irradiate a column of as much as one million tons of water that would fall out over an area of several miles—severely contaminating ships and land areas within that zone.[3] But a 10-kt airburst from a missile would be more destructive (akin to the 15-kt “Little Boy” bomb used on Hiroshima) because so much of the energy of a UUV-based nuclear explosion is contained under water.
Deployment and basing. Assuming Pyongyang actually deploys the Haeil, we do not know how many might be fielded or how it might be based. The UUV would quite likely be deployed in hardened shore installations akin to coastal defense torpedo-launching sites that would be heavily camouflaged and/or disguised as civilian or other benign installations. Because the Haeil could be hidden in such facilities before launch, it could be fairly secure from pre-launch attack, barring a fortuitous allied intelligence coup.
It also is possible that Haeils could be towed out to sea by North Korean ships, as noted in the March 24 statement, during a prewar crisis or prior to an attack decision. The ship (perhaps a commandeered civilian vessel) could either drop the UUV off at sea or stay tethered to the UUV for subsequent launch. This approach would increase allied opportunities to detect the UUV in transit or at its sea holding area, however, compared to land basing. It also would be harder to ensure launch commands were received, especially in wartime, unless the UUV was still tethered to a ship and the ship had not previously been attacked.
Limited Threat Potential
The Haeil would be inferior to North Korea’s nuclear-armed ballistic and cruise missiles in terms of speed (and thus time-to-target), accuracy, and lethality; furthermore, it is limited to in-theater coastal targets. Although it would not be subject to allied air and missile defenses, it would be at risk of detection and engagement by ASW assets. A slow, battery-powered UUV would probably be quieter, and thus less vulnerable to acoustic detection, than North Korea’s conventional submarines, but we do not know how quiet the Haeil is relative to allied detection thresholds.
Not much anti-ship capability. The March 24 statement referred to attacking “naval striker groups.” The Haeil appears to be too slow to pose a viable threat to ships that are underway. It would also need to have an on-board capability to detect such groups itself and/or a way to receive and act upon external targeting information—data that would be challenging for North Korea to obtain, especially in wartime. And both capabilities could increase the UUV’s vulnerability if used. Therefore, Haeil’s threat to shipping probably is limited to ports and known anchorages.
Unlikely first-strike weapon. The UUV’s extremely slow speed, forcing it to face many hours of potential ASW detection risk before reaching target, makes it unlikely that North Korea would consider using the Haeil alone to conduct a surprise nuclear attack or as an attack precursor, or timing the Haeil’s arrival to coincide with that of an initial nuclear missile strike. Moreover, it is not clear whether North Korea can communicate (or communicate reliably) with the UUV once underway to cancel an impending attack if circumstances change during its many hours of transit. Once even conventional hostilities begin, North Korea’s land-based means to communicate with a submerged UUV are likely to be taken out.
Suitable for delayed retaliation. More likely, the Haeil would be launched at the same time as a nuclear missile strike—particularly if the North was a) initiating nuclear use; b) preempting what it strongly believed was an imminent allied nuclear attack or an attempt at a disarming strike against its missile force; or c) retaliating against such attacks, either while the attacks were ongoing or after the fact. The damage caused to allied ASW and command-and-control by the earlier arrival of North Korean missiles probably would increase the Haeil’s ability to avoid interception if successfully launched. But most of the damage from a North Korean retaliatory strike would already have been done by missiles long before any Haeils arrived.
A limited “dead hand.” Pyongyang might also see the Haeil as a “dead hand” option, ensuring some sort of nuclear retaliation in the event that a) an allied disarming strike against its missile force was somehow successful, or b) North Korea had lost, or was doomed to lose, a conventional war or had suffered nuclear devastation. A successful last UUV strike would be far from assured, however, given allied ASW capabilities. And the limited, albeit terrible, impact of 10-kt coastal strikes against a country with so much of its population and industry inland may not offer North Korea what it regards as sufficient comfort or satisfaction.
More Political Than Military Value
Based on what we can divine from open sources on the Haeil’s capabilities and military potential, the South Korean JCS’s March 27 assessment that “it is highly likely that these claims are exaggerated and manipulated” appears to be correct. As is often the case with North Korea, the UUV seems to have much more political than military utility. Future, more capable follow-ons to the Haeil cannot be ruled out—and perhaps the North was hinting at this by adopting the “Haeil-1” nomenclature on March 28—but battery-powered UUVs are unlikely to offer any military advantage in nuclear delivery over North Korea’s ballistic and cruise missile forces.
Politically, however, the unveiling of the Haeil is consistent with the past several years of Pyongyang’s force development and related public diplomacy, which it has used to message that:
- North Korea has large and diverse nuclear delivery capabilities (referred to on March 24 as “the more developed, multi-faceted and offensive nuclear attack capability,” and on March 28 in “the strategic plan…on combining and operating nuclear weapons by different means in the diversified operation spaces”);
- Allied attempts at preemption, decapitation and missile defense will, therefore, be unsuccessful, and North Korean nuclear retaliation cannot be avoided, especially against South Korea; and
- North Korea is highly technologically capable and can build the same kinds of weapons the major powers can.
All of these themes come together in North Korea’s clear effort to introduce the Haeil in a way that evokes Russia’s Poseidon UUV—down to the claim of being able to generate “a super-scale radioactive tsunami.” Unlike the Haeil, however, the Poseidon is very large (at least 1,500-mm diameter), nuclear-powered, has very deep diving, high speed (over 50 knots), intercontinental range nuclear warhead, and is armed with at least two megatons (with claims of 100 megatons, although even that could not generate a “tsunami”).
The Bottom Line: A Political Statement Posing a Limited Threat
As other analysts have concluded, North Korea is unlikely to deploy very many Haeil UUVs and will continue to rely on ballistic missiles for the bulk of its nuclear strike capability. As a nuclear delivery system, this UUV brings little to the table due to its slow speed, potential in-transit vulnerability to ASW, and limited attack capability. The Haeil is much more valuable to North Korea as a political messaging tool, although even a good part of that value may already have been gained simply through unveiling it. It remains to be seen how much more Pyongyang invests in this venture.
- [1]
See Colin Zwirko, “North Korea shows off smaller nuke warhead it says fits on missiles aimed at ROK,” NK News, March 28, 2023, https://www.nknews.org/2023/03/kim-jong-un-inspects-warheads-as-part-of-push-to-produce-more-nuclear-material; and Jeongmin Kim, “North Korea ‘exaggerated’ about new undersea nuclear drone, Seoul says,” NK News, March 27, 2023, https://www.nknews.org/2023/03/north-korea-exaggerated-about-new-undersea-nuclear-drone-seoul-says.
- [2]
- [3]
See David Albright, “Underwater Nuclear Drone: North Korea’s Nuclear Madmen,” Institute for Science and International Security, March 27, 2023, https://isis-online.org/isis-reports/detail/underwater-nuclear-drone-north-koreas-nuclear-madmen; and Samuel Glasstone and Philip J. Dolan, The Effects of Nuclear Weapons (Washington, DC: US Government Printing Office, 1977), 52 and 54, https://www.atomicarchive.com/resources/documents/effects/glasstone-dolan.html.