Bunker Busting North Korea's Nuclear Program

Although Iran hasn't demonstrated a working nuclear device, the country was believed to have had one of the most protected nuclear programs in the world with its range of air defense sites and numerous underground facilities. But following the June 2025 Israeli attacks on Iranian conventional military and nuclear infrastructure, backed up by the United States dropping fourteen "bunker buster" bombs on two key underground facilities, Iran's nuclear program has likely been knocked back by several years.

U.S. Air Force airmen inspect a GBU-57 Massive Ordinance Penetrator at Whiteman Air Base, May 2, 2023. Image: USAF 

North Korea, too, has an extensive network of underground sites to support what is the most well-developed nuclear program of the world's traditional "pariah" states. In fact, it may have more underground facilities than any modern country except (perhaps) China. And unlike Iran, North Korea has proven that it has developed nuclear devices. So, finding ways to limit or even remove Pyongyang's nuclear capabilities is something Western governments have considered for years. 

In light of the unprecedented use of the GBU-57 Massive Ordinance Penetrator (MOP) "bunker busters" against Iran's Fordow and Natanz nuclear sites, could they be used against North Korea's nuclear facilities?

A quick primer on these bombs and their capabilities. The GBU-57 MOP was the result of a US Air Force development program from 2002 to create very large conventional explosives. First tested in 2007, the first deliveries of the finalized MOP took place in 2011. 

These bombs weigh 12,304 kg (27,125 lbs) and are designed to be dropped from the B-2 Spirit 'stealth bomber' - the only aircraft in the world capable of carrying the bombs. Through the use of precision guidance systems and a "smart fuse", the bombs can be dropped on a target and detonate at a pre-determined depth. 

The exact penetrative capability of the MOP is classified but it is generally believed to be capable of penetrating 60 m (200 ft) of "ground" (what that means exactly is unspecified) and 18 m (60 ft) of reenforced concrete. However, the density of the overburden rock (limestone vs basalt) and the compressive strength of the concrete used at a target facility could dramatically impact the bomb's performance and damage.

In the case of the Iranian nuclear facilities that were bombed, parts of Fordow are estimated to lie more than 80 meters below ground, however, the bombs targeted ventilation shafts that led from the surface and may have given the bombs an easier path through the mountain into the underground facility.

So how prepared are North Korea's underground facilities to weather such an attack?

North Korea has thousands of underground sites but only a few dozen are associated with the country's nuclear and ballistic missile programs. 

However, the core of the country's nuclear infrastructure is made up of facilities that are actually out in the open.

The Yongbyon Nuclear Scientific Research Center with underground sites and tunnels highlighted.

The Yongbyon Nuclear Scientific Research Center is North Korea's crown jewel. It has two nuclear reactors, two uranium enrichment buildings, and a radiochemistry laboratory where plutonium can be produced. Yongbyon has underground sites, but the bulk of its enrichment and radioisotope production capabilities are all located above ground. What underground components do exist are relatively small and do not appear to be positioned particularly deep underground.

Newly built suspected uranium enrichment building at Yongbyon.

Even Yongbyon's newest suspected uranium enrichment building, built in 2024-2025, sits proudly in the open with a striking blue roof. A review of satellite imagery during the construction process also shows that it lacks any underground rooms and so is quite vulnerable to traditional air and missile strikes.

The Kangson Uranium Enrichment Plant.

And then there is the Kangson Uranium Enrichment Plant. Located just a few kilometers away from Pyongyang, there are no known underground parts of the plant. The use of reenforced concrete and advanced concrete formulations can, of course, make buildings much more secure. But North Korea hasn't employed the German WWII strategy of making "indestructible" buildings using hundreds of thousands of cubic yards of concrete, and they aren't known to have developed any particularly pressure resistant concrete that could deflect a direct hit from a missile. 

Thus, an adversary wouldn't need to use special ground penetrating munitions to destroy those two sites, just typical cruise or ballistic missiles. This is a critical vulnerability as destroying Yongbyon and Kangson would also prevent North Korea from producing any plutonium or from enriching enough uranium following the attacks to produce new warheads.

But there are also secret facilities that are buried beneath mountains that are rumored to hold their own centrifuge cascades and could serve as backups to Yongbyon. The two facilities that have the most supporting evidence are Kumchang-ri (40° 7'8.96"N 125° 8'28.77"E) and Hagap (40° 4'53.90"N 126°11'23.03"E). 

Kumchang-ri Suspected Nuclear Facility.

Kumchang-ri is a sprawling complex north of Kusong that was first made public in the 1990s. An American delegation was actually permitted to visit Kumchang in 1999 and in 2000 and they reported that although there were 6 miles of tunnels, the site was empty, and that its layout may not be suitable for an underground reactor facility or for running enrichment activities.

Since then, work at Kumchang has slowed dramatically. And periodic monitoring by public sources using commercial satellite imagery does not reveal any major changes that would suggest it's operational, either as a nuclear site or any other industrial purpose. 

The external grounds of Kumchang are maintained as are the surface buildings, but vehicle traffic is sparse, and there are no obvious signs of the large-scale electricity supply needed to run centrifuge cascades, no water treatment facilities, and only enough nearby housing to support a handful of workers.  

But could Kumchang be cracked open by bunker busters?

The US attack on Fordow used the facility's design against itself. The bombs were aimed at ventilation shafts that led from the surface of the mountain into the facility itself. These shafts provided more direct access to the interior and would have allowed more of the blast power from the bombs to spread instead of being absorbed by the overhead rock.

At Kumchang, there are no apparent ventilation shafts or any other access points except for the ground-level entry tunnels. This may be because construction was never completed or because they use a different technique for bringing in fresh air. Additionally, the facility is protected by up to 210 meters (690 ft.) of rock at its deepest and that means the GBU-57s would only be able to penetrate the flanks of the facility, where there is less rock protecting it.

Given what is publicly understood about the interior of Kumchang, such an attack would still likely do enough damage to render the site unusable in the short- to- medium term.

The Hagap Underground Facility.

Likewise, the Hagap Underground Facility is buried deep within a mountain and no clear visual evidence of ventilation shafts exists. Hagap's facilities are protected by between 65 and 215 meters (213-705 ft.) of rock, depending on which part of the UGF is being targeted. This would suggest that Hagap may be able to withstand an attack by GBU-57s, except for the various tunnel entrances that are at the surface. 

At least three large entrances exist, spread out along a line 800 meters (2,624 ft.) long, and work at Hagap has been ongoing for 30 years, potentially giving Hagap a more complicated interior layout than Kumchang. If Hagap is indeed a nuclear-related facility (and there are questions about this), without solid intelligence as to its design, confidently destroying the facility may require hits by six or more GBUs.

General diagram of how bunker busters work. Image: US Department of Defense.

Nuclear Assembly, Storage, and Delivery Facilities

Unlike Iran, North Korea has a proven nuclear capability. So, preventing Pyongyang from future development and also using what nuclear devices they already have is part of contingency planning in the event of an open conflict. 

Addressing the country's existing arsenal would be the most pressing issue and, I believe, the most difficult because there doesn't appear to be intelligence as to where every individual nuclear weapon is located, and North Korea does maintain numerous suitable sites for storage and missile launches. 

In terms of the GBU-57s, this poses a particular problem because, after the Iranian attacks, the US now only possesses another dozen or so of the munitions and manufacturing new ones would not be easy.

Tunnel entrances at the Yongdoktong nuclear facility before they were covered by a building in 2020.

The Yongdoktong nuclear complex (40.004721° 125.339239°) is believed to be where North Korea develops the high explosive lenses used to detonate nuclear devices and where the country assembles the final warheads. Additionally, Yongdoktong is believed to be North Korea's primary (if not sole) nuclear warhead storage facility. 

The complex does have several underground sites. The most prominent UGF (imaged above) is protected by less than 65 meters of rock for much of its area and so could be vulnerable to bunker busters. A level of uncertainty exists with attacking Yongdoktong because North Korea's nuclear command and control protocol isn't fully understood.

The country could hold all of its nuclear weapons in a single repository, only sending out warheads when personally ordered by Kim Jong Un. Or it could be the primary storage site but a small number of warheads may also be deployed to strategic missile bases around the country so that they could be quickly mated onto a missile and launched whenever ordered. These bases, 15 to 20 of them, would also require penetrative ordinances to fully destroy.

Underground entrances at the Kumchon-ni Ballistic Missile Base. The image used is from 2003 because it more clearly shows the entrances. The site looks little changed today.

The country is also dotted with thirteen hardened and underground submarine bases as well as twenty air bases with underground facilities. 

Onchon Air Base, with its distinctive T-shaped runway that is partially underground.

The Ryoho-ri submarine base at the East Sea Fleet Command.

However, the underground submarine bases would likely struggle to accommodate North Korea's only nuclear-capable ballistic missile submarine, the Hero Kim Kun Ok Class which, at 86 meters in length, is 10 meters longer than the Romeo Class which was North Korea's largest submarine class. The Hero Kim Kun Ok instead is openly berthed at the Sinpo Submarine Base; its only defense against most forms of attack would be to take to the sea.

And since North Korea doesn't have an air-based nuclear delivery system, there are no nuclear-capable bombers to hit hiding in underground air bases.

In conclusion, North Korea has a widely dispersed nuclear program. That alone makes it a more difficult problem to address militarily. But, if the United States or some other country wanted to prevent North Korea from producing additional nuclear material, that could be accomplished through the use of Tomahawk missiles or other non-bunker busting munitions. 

Although North Korea has a massive underground infrastructure, they have elected to put all of their most critical nuclear material producing facilities above ground. 

At the same time, if the United States wanted to confidently launch a strike against the country and prevent North Korea from using their present nuclear arsenal, that becomes a much different proposition.

The number of potential hardened storage sites that would likely need to be hit would deplete the entire current inventory of GBU-57 MOPs, and even then, some sites would still exist. Without exceedingly accurate and detailed intelligence, the risk of striking North Korea's nuclear infrastructure only to have them fire a nuclear-armed missile back at the United States is too great. 

The fact we haven't struck against North Korea's nuclear program suggests that the risks are indeed too great (both in terms of nuclear retaliation and the risk of an attack against Seoul) and that the intelligence is, more than likely, simply not there to adequately support such a wide-scale attack. 

In my personal view, the last chance to kinetically engage was back in the early 2000s and maybe even 1990s. Bunker busting bombs or no, now that North Korea has a proven nuclear capability and numerous places to store warheads, missiles, and other equipment, even if such weapons could destroy any individual nuclear-related site, there is currently no way to guarantee North Korea wouldn't or couldn't launch a retaliatory strike from other locations. 

I would like to thank my current Patreon supporters who help make AccessDPRK possible: Donald Pearce, David M., Dylan D, Joe Bishop-Henchman, Joel Parish, John Pike, Jonathan J., Kbechs87, Raymond Ha, Russ Johnson, Squadfan, and Yong H. 

--Jacob Bogle, 8/25/2025

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Kim Jong Un's Underground Pyongyang

Verifying the existence of underground facilities can be a difficult task, especially when their existence is a state secret. But rumors eventually come out and tantalizing hints of their presence can sometimes be found.

For North Korea, these rumors tell of secret subway lines beneath Pyongyang and underground highways connecting major palaces, maybe even reaching as far north as the border with China. I have written quite a lot about North Korea's underground infrastructure, but direct evidence and declassified sources still remain scarce. 

Overview of the Pyongyang Government District.

However, within the secured government district of Pyongyang are signs of multiple tunnels and underground structures. While it's impossible to know how they all connect to one another or even if they do, their locations and prevalence do hint at a fairly robust underground network that supports the infrastructure, transportation, and security needs of Pyongyang's most important district.

The easiest way to identify underground facilities is to either spot their entrances or actually catch them being constructed. For the secured government district, most of the buildings were constructed decades ago, placing their secrets out of reach for those without security clearances. But under Kim Jong Un, there have been some substantial changes to the district and that has given North Korea watchers an opportunity to see observe some of them.

There are two main sets of tunnels within the 138-hectare district that are visible to satellite. The first is a set of four tunnels near the Central Committee Office building (also known as Kim Jong Un's office) and the adjacent villa (Residence No. 15). The second is a set of four tunnels leading to underground parking garages beneath three buildings that were constructed in 2018-2019.  

There is also a possible tunnel, marked in light blue, but I can't fully verify that it is a tunnel. In some images, however, it appears that there may be a road tunnel that dives under a gate near Kim Kyong-hui Hall, just south of Changgwangsan House.

But the tunnels around Kim Jong Un's office and Residence No. 15 are quite clear.

April 10, 2020 image of the four tunnels around the Central Committee Building (Kim's office) and his district villa, Residence No. 15.

Apart from the tunnels by the villa and office, which I'll detail next, there is also a smaller tunnel in the maintenance complex. This complex handles building heating and cooling equipment, provides maintenance services, and may also play a role in electricity and water supply to the adjacent buildings. The tunnel (39.016557° 125.743544°) is 5-6 meters wide and runs toward the southwest. It's visible on all satellite imagery going back to 2000.

The tunnel may simply lead to a hardened bunker housing additional equipment or it could actually connect into the Office 39 complex (which includes the Kim Il Sung Revolutionary History Institute [39.016134° 125.741890°] and other Party buildings). Given its size and location, I do not think this tunnel plays any special security role. Rather, it's most likely just an access tunnel for providing building services.

April 1, 2023 image showing changes since 2020.

In 2022 a villa was rebuilt and enlarged, and in late 2022 a new hardened structure was built over the site of the tunnel nearest Kim's office building. 

The 'office tunnel' is large enough for vehicles and may lead to an underground garage or a larger underground complex. The hardened structure above it is approximately 60 by 30 meters in size and rises approximately 3 meters above the surrounding gardens.

Conjectured tunnel layout.

Due to the number of visible entrances, a concept of the tunnel layout can be formed with some confidence despite not having all the information. 

The covered walkway from Residence No. 15 was constructed in 2010. It resembles another such walkway that was built in 2017 in the armed forces district 5 km north at 39.062677° 125.740196°. 

The southern tunnel entrance was also constructed ca. 2010-11. Following the path drawn in the above image, the southern tunnel is about ~150 meters from the northern tunnel at the Central Committee Office Building (CCOB). 

The northern tunnel, however, was only constructed in 2018. This means that the southern tunnel likely went directly to the CCOB, where an alleged 60-car garage also exists beneath the assembly hall. 

This connection allows people from Residence No. 15 to travel on foot or by car directly and safely to the CCOB. Then, in 2018, a new tunnel was built from the CCOB that would link up with the southern tunnel.

This construction also included the building of an underground structure which was later (2022) replaced by the 60 x 30-meter hardened structure now seen in satellite images. Allegedly, a small, electrified rail car is also employed within the tunnels, but I haven't seen any supporting evidence of that.

To the north of the Central Committee Office Building, between 2018 and 2020 four currently unidentified buildings were constructed. These buildings include glass-covered entrances to underground parking garages that, most likely, would also double as bomb shelters in the event of an air attack.

Underground garage entrances under construction in June 2020.

The underground garage entrances after completion are covered by glass canopies.

There are also reports (including from Hwang Jang-yop) that the Pyongyang Metro has a secret line for government use that connects important government and military installations around the capital, and that it even reaches as far as Nampo and Sunchon (50 km away). While this has never been independently verified, the government district does lie within 2 km of four subway stations, with the closest being Pongwa Station at only 600 meters away from Kim's office.

As most of the district was constructed in the 1960s and 1970s (as was the metro), underground entrances to the metro system could be hidden beneath key administrative buildings, beyond the prying eye of today's satellite fleet. I have doubts about a sprawling network of transportation tunnels connecting far flung facilities, but a local network connecting underground command centers and emergency escape routes is quite plausible. 

Location of other known tunnels and underground facilities (UGF).

Whether underground sites exist in isolation or connect to larger tunnel networks beneath the government district and beyond, the sheer number of bomb shelters and other underground facilities alleged to exist makes the possibility of a successful "decapitation strike" by South Korea or the United States far more difficult and less likely to be effective, as such an attack relies on knowing where the target individuals are and killing them before they have time to escape to another location.

While I can't comment as to the quality of their construction, as a regime hyper-focused on survivability, North Korea probably has the greatest density of underground facilities and secret tunnels of any country on earth. 

I would like to thank my current Patreon supporters who help make all of this possible: Alex Kleinman, Amanda Oh, Donald Pierce, Dylan D, Joe Bishop-Henchman, Jonathan J, Joel Parish, John Pike, JuneBug, Kbechs87, Nate Odenkirk, Russ Johnson, and Squadfan.

--Jacob Bogle, July 24, 2023

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The Largest Underground Sites in North Korea

Kim Jong-un visiting the Kanggye Tractor Plant. Image: Rodong Sinmun, June 2013.

There are over 2,500 underground sites in North Korea that have been publicly verified. They fall into five main categories: Hardened artillery sites, underground factories, underground storage facilities, underground air bases, and the underground facilities at missiles bases. There's also the large underground nuclear test site at Punggye-ri, several underground navy bases, and some others that are used for communications and emergency command sites, but those only make up a small number of the overall sites.

Other estimates place the number of underground facilities (UGF) as high as 14,000, but that would include everything from civilian bomb shelters to not-exactly-underground covered bunkers. And things like bomb shelters beneath apartment buildings isn't something that using commercial satellite imagery can easily work out.

So, of the ~2,500 UGFs that I can directly point out to you, a few stick out as being exceptionally large.

A note on estimating sizes. There are several fairly easy ways to estimate the size of an underground facility. The simplest of which is to look at the spoils dumped outside. Measuring the width and height of the rock piles can give you an idea of the volume being excavated. You can also consider the purpose (if known) of the UGF and what it might require in terms of size, you can look at the distances between entrances and service adits, and take into account the geology of the hill/mountain being tunneled into. 

Unfortunately, many North Korean UGFs don't have spoil piles to examine; the debris having been carried away to better hide the size of the facility. And looking at the distances between entrances only tells you that a tunnel exists, not necessarily a large complex with multiple floors and a warren of passageways.  

And, unlike underground airbases or artillery sites, not every UGF in the county has been assigned a purpose within open-source intelligence. That adds another layer of difficulty in estimating the size of a facility.

Therefore, this list comes with a few limitations. But whether or not this list contains the literal 14 largest UGFs (excluding missile bases) they are nonetheless among the largest in country. Some are rather astounding in size, at least to me, considering the state of North Korea's technology and the tools and skills they have available.

With that in mind, here are 14 of the largest underground facilities in North Korea.

Arms factories

The Kanggye General Tractor Plant (40°57'28.72"N 126°36'22.75"E) is the largest underground arms factory in North Korea. Also known as Factory No. 26, it was established soon after the Korean War after the original small-arms factory was split into three, and each part moved to different areas of the country.

The term "tractor" comes from Soviet nomenclature that typically denotes a military factory, with tractors rarely being made at "tractor" factories. Mortar ammunition, rifle ammunition, and self-propelled artillery ammunition are among the more common items produced at the factory, but they are also responsible for manufacturing short-range missiles.

Externally, the factory covers around 99 hectares. However, the factory has multiple underground entrances that provide access to the interior of a 1.8 km-long hill. While the exact size of the plant isn't known, the height of the hill would allow for multiple factory floors and several kilometers of tunnels.

It is estimated that the plant employs at least 20,000.

One of its biggest chapters occurred on Nov. 30, 1991, when an explosion rocked the factory.

Before and after images from Google Earth/Landsat showing a large area of land disturbance indicative of an explosion and clean-up efforts.

A mishandling of explosive material led to a small fire that eventually spread and caused a major explosion. Officials shut down communication in the area to stop news of the explosion from spreading and the disaster has never been publicly acknowledged. 

However, Landsat imagery from the time does show that something major happened at the factory.

Based on measurements of the imagery, the explosion destroyed an area nearly a kilometer wide and likely damaged every above ground building in the factory complex as well blew out windows for kilometers around. 

It has been alleged that the explosion killed around 1,000 people. If true, that would make it one of the deadliest defense industry-related disasters in history, perhaps only second to the 1917 Halifax Explosion which killed nearly 1,800.

It took 3-4 years for the site to be cleared and reconstructed, and, possibly as a legacy of the explosion, no new residential buildings have been constructed facing the factory, although the area does remain populated.

Panghyon Aircraft Factory (39°53'6.52"N 125°13'56.52"E)

First constructed in the 1960s, this factory used to be North Korea's only aircraft factory and it is still the primary factory that produces replacement parts for the country's fleet of aging MiGs and J-6 copies.

The factory is nearly 1.5 km long and is positioned around a hill. The primary underground entrance is ~14 meters wide and with 91 meters of overburden, a very large underground factory could exist, occupying upwards of 100,000 sq. meters.

It is believed that during the 1990s and early 2000s centrifuges for uranium enrichment were manufactured and stored at the factory, with as many as 300 centrifuges being held there. This provided a critical industrial component to North Korea's nuclear infrastructure. There is no indication that the factory is still produces centrifuges today. 

Panghyon has also been the site of ballistic missile launches including a Hwasong-14 ICBM launched on July 4, 2017.

Tonghungsan Machine Plant (39°57'11.97"N 127°32'48.35"E)

Tonghungsan is a large factory that is suspected of producing missile components and parts for mobile launchers. It is split into two main sections, above ground production facilities and the underground complex.

The above ground part of the factory has been undergoing a complete reconstruction since 2016 and now includes 19 production-related buildings, 11 administrative and support buildings, and the reconstruction also involved building 31 residential buildings and several other structures such as schools and cultural/communal sites.

The construction also extended to the entrance and security buildings that lead to the underground entrance. The primary entrance has two portals that are 60 meters apart. A service adit (portal) is visible 140 meters north and piles of excavation spoils can also be found 400 meters from the main entrance, and another pile is 820 meters away. Yet another adit is also located on the other side of the mountain, 1.3 km away from the entrance at 39°57'45.31"N 127°32'13.21"E.

Simply connecting these visible parts of the UGF suggests that there could be at least 291,000 sq. m. of underground space. If there are multiple levels, that could reach upwards of 400,000 sq. m. given the area's geology. Of course, large underground facilities aren't massive single caverns. They have galleries (halls), support structures, and may need to avoid weak spots in the rock, so the real size of usable space will be less than 400,000 sq. m., but it could still be the equivalent in size to an automobile factory or the Louvre Museum, all beneath a mountain.

Major Underground Airbases

Twenty-one North Korean airbases have underground facilities, but the following six bases represent the largest in terms of the underground tunnel length and the amount of possible internal space.

Koksan AB (38°40'34.89"N 126°35'40.69"E)

Koksan AB consists of a single 2,496-meter-long runway and is home to the 86th Air Regiment and stations twenty-four MiG-21 fighter jets at the base. 

The underground facility employs two main entrances for jets to enter beneath a mountain that rises 120 meters above the facility. The entrances are ~185 meters apart and there is also a service access tunnel that's ~600 meters to the south of the main entrance. This suggests that the Koksan UGF could have 96,000 sq. m. of underground space.

Nuchon AB (38°13'52.09"N 126° 7'43.57"E)

Nuchon consists of a single 2,495-meter-long runway and is home to the 32nd Air Regiment (fighter-bomber) and is home to several J-5/MiG-17, MiG-21PFM, Mi-2 aircraft.

The tunnel connecting the two underground entrances is 575 meters long. At a minimum, the UGF covers 18,450 sq. m. but the hill above contains enough overburden to support a theoretical UGF up to three times that size if there are galleries that branch off the main tunnel.

Onchon AB (38°53'13.32"N 125°16'29.39"E)

Onchon is unique in that it has the only fully functional underground runway in the country. The base's primary runway is 4 km to the west.

Onchon is home to the 36th Air Regiment (fighter). At least 36 aircraft are stationed at the base.

The underground complex consists of an underground runway, with 700 meters of it going underground, and two underground entrances used to bring aircraft inside of repair and storage facilities. The two entrances are 280 meters apart.

Connecting the entry tunnels and underground runway area together would yield a UGF of 51,800 sq. m. If the internal layout is more complex with extra galleries, the theoretical maximum size grows to roughly 160,000 sq. m. 

Pukchang AB (39°30'44.60"N 125°57'28.76"E)

Pukchang is home to the 58th Air Regiment (fighter) and 60th Air Regiment (bomber) and has MiG-23MLs and MiG-21Bis stationed at the base; with upwards of 60 aircraft being stationed here at any given time.

Pukchang has three underground entrances that are spread out by 400 meters. I suspect that the internal layout of the UGF is fairly simple and does not greatly expand into the hill any more than what's needed to connect the three tunnels and provide some extra storage/maintenance space. This gives an underground area of 11,000 sq. m. at a minimum but likely no more than 16,000 sq. m.

Taetan AB (38° 7'3.70"N 125°13'21.97"E)

Taetan Airbase is home to the 4th Air Regiment (fighter) and has two runways. One is 2,810 meters long and the other is 2,490 meters. The UGF entrances are ~1.3 km away from the runways.

The two underground entrances are ~540 meters apart. Reviewing the area, I think the UGF consists of a single large rectangular structure (built from the tunnels and 'inward' toward the south) with no side galleries or other structures beneath the hill. A straight-line tunnel directly connected to the entrances yields and area of 19,000 sq. m. The surmised rectangular UGF would occupy 59,000 sq. m. There is no visible evidence of access adits or spoils from excavations further into the hill that would suggest a substantially larger facility.

And lastly, Kang'da-ri AB (39° 5'48.78"N 127°24'51.67"E)

Like Onchon, Kang'da-ri also has an underground runway, but the facility doesn't appear to be actively used by aircraft, leaving Onchon as the only active underground runway in North Korea.

The Kang'da-ri complex consists of a primary runway on the left bank of a river and an underground runway. The primary runway was modernized in 2009/2010 but has since been abandoned and left to deteriorate each time the river floods. 

The underground history of Kang'da-ri goes back to 1998 when the initial excavations into the small mountain began. Work has carried on in fits and starts, with the most recent work appearing to have stopped in 2018.

The paved portion of underground runway is 1,748 meters, with ~750 meters of that actually being underground. 

It has been claimed that the base is part of the 2nd Air Combat Division, but no aircraft can be seen in any of the images available on Google Earth. Additionally, Joshua Stanton has said that the runway is too small for fighter aircraft. 

The true purpose of the base is unknown, but part of North Korea's chemical weapons program is said to be based at Anbyon, a town just 11 km away. However, there are few military facilities at Anbyon that would be suitable for chemical weapons storage, but the underground Kang'da-ri runway is protected by large blast doors and it cannot be directly accessed by any major highway - adding to the site's security. So I think the base is a candidate location for weapons' storage (chemical or otherwise), particularly since the government has seemingly taken 24 years to build an incomplete "airbase".

Unidentified large UGFs

Hagap UGF (40° 4'54.23"N 126°11'22.74"E)

Hagap has been written about extensively (including on this site here & here), but it is in this section because we still don't know what the place is actually supposed to be. The two prevailing theories are that it's either an underground uranium enrichment plant or that it is part of the national archives.

The enrichment theory was put forward the moment Hagap became publicly known about in 1998. Given the construction of the Kangson enrichment plant near Pyongyang, and that Hagap still has not been completed, it would make its existence redundant (and very expensive) as an enrichment site. However, it could play any number of other roles within North Korea's nuclear program.

The other theory put forward is that it is meant to ultimately become an archives facility capable of protecting the most important documents and artifacts from even a nuclear blast.

After several years of apparently being dormant, new construction began at Hagap in 2011/2012 with a new underground entrance being excavated and the spoils were used to lay the foundation for an access road. This work was carried out methodically until in 2015/16 the pace of construction was sped up and new work could be seen throughout the eastern side of the complex. 

This construction coincided with underground work being carried out at the International Friendship Exhibition located a short 8 km away. The IFE is where North Korea houses the countless gifts, medals, and awards given to the country's leaders over the decades and is used in propaganda as proof of the greatness of the Kim family. 

Concurrent construction at both sites could merely be coincidence, but I think it might add a little weight to the theory that Hagap is actually meant to be part of a highly secured national archives, perhaps holding the true histories of Kims and government that are too dangerous to be accessed by anyone but the most devout followers of Juche or that it will hold the foundational documents and artifacts of the country to protect them from war or natural disaster.

Based on the locations of the underground entrances, there is a primary tunnel capable of handling vehicle traffic that runs for ~500 meters. The facility very likely also extends within the mountain for another 400-500 meters.

Sonjesan UGF (39°18'46.95"N 125°55'33.74"E)

Sonjesan is an interesting site. It is located in a random hill halfway between Pyongsong and Sonchon. It has no obvious industrial infrastructure or particularly tight security. At the same time, the roads leading to the UGF also go through multiple nearby military facilities, and it has four entrances.

The main entrance is at 39°18'46.95"N 125°55'33.74"E but the above image is centered on the two rear entrances at 39°18'35.52"N 125°55'50.47"E because they show up the clearest in the available imagery.

Connecting the four entrances into a simple rectangle yields a potential area of 95,700 sq. m., that's over a million square feet. Sonjesan also has visible spoils piles and examining those shows that at least 100,000 cubic meters of material has been excavated out of the hill. 

In 2020, the original buildings at the main entrance were demolished and new ones built. Another point of excavation that is almost certainly connected to the primary UGF was also opened in 2016, with the spoils pile growing each year into 2021. The pile contains approximately 6,300 cubic meters of material.

A nearby sixth site was constructed in 2017/18 at 39°18'14.84"N 125°55'40.66"E, along with a new military base, but I'm not sure if this tunnel connects to the main facility or if it's simply its own small UGF. 

Taedonggang UGF (39°10'25.07"N 125°56'43.60"E)

Located by the Taedong River, near the Kangdong Leadership Residence, its four entrances are spread out along nearly 300 meters and the site could also be connected to a large artillery position 520 meters away that itself has an underground component. 

The four entrances are grouped into two groups and I don't think they're connected to each other. So the actual underground facility may not technically be among the largest because of this, but the overall complex itself it rather large. The particular layout of the UGFs is also uncommon.

The roads leading to the entrances are also quite wide and would allow access to vehicles that have wide turning radii such as missile launchers or large artillery systems. 

Interestingly, at the end of the base is a large overhead crane, such as one might see at a containership port or factory. New buildings were added at the crane site in 2019. The presence of the crane could suggest that the base is, in fact, used more for storage and maintenance (perhaps even of industrial equipment) than as an active missile or artillery base. 

 

Abandoned/Unsused UGFs

The Kyongje-dong Bunkers 38°34'36.46"N 125°56'8.15"E

The bunker complex at Kyongje-dong are one of the more enigmatic facilities in North Korea. The two bunkers are much too large to have been purpose-built for missile launchers, they don't extend deep enough into the hillside to be a typical storage facility, and they aren't part of a factory or other industrial infrastructure. 

Joseph Bermudez and Victor Cha over at the Center for Strategic and International Studies helped to shed a good deal of light on the bunkers. It is perhaps the most detailed open-source report on them.

The initial preparations for construction took place in the 1980s, but primary excavation work began in 1993. The facility was completed in 1998.

The two bunkers have entrances 40-meters wide, and they each have a large concrete pad in front that measures 60 by 40 meters. The entrances are protected by blast doors, and the earth-covered bunkers themselves are approximately 60 meters long.

The CSIS report goes on to say that the facility is most likely a reserve site that would serve as a forward operating base for MD-500 helicopters in the event of war, allowing special forces operations to penetrate much further into South Korean territory than other existing heliports would allow.

Hamhung abandoned UGF - 39°59'50.27"N 127°42'52.09"E

This site is 17.5 km northeast of downtown Hamhung. When I first came across it, I thought it was a mine, but a closer inspection of the main area reveals what is apparently a large tunnel protected by what can only be described as blast doors.

Looking at historical imagery on Google Earth shows that work began at the site in 1996 and work was ongoing in 2008. The UGF sits at the end of a valley, with the rest of the valley filled with numerous support buildings spanning 1.7 km. But by the early 2010s, work was halted. Nearly all of the buildings were then removed in two phases, one in 2016 and the other in 2021.

The primary tunnel face is ~45 meters wide and there is what looks to be a large metal frame to hold protective doors. A second entrance was created but has since been closed, possibly as the result of rock collapsed. 

The crane that was used to move materials into dump trucks has been kept in place.

It's still possible that the site used to be a mine, but if so, its design is unique in North Korea. If it was meant to be an underground facility, I think geologic problems developed as they dug deeper into the mountain, perhaps causing severe leaks or internal collapses. This wouldn't be the first time a UGF in the country had to be abandoned due to collapse. A coastal defense battery had a large cave-in back in 2016.

I also want to add an honorable mention to the network of tunnels that protect the Kim family. These road and rail tunnels connect various palaces and military command centers together, enabling the Kims to move around the country securely during a time of war or to evacuate one place and get to another. Most of this network is still hidden but there are some known/suspected parts of it that rise to the surface and can be seen by all.

One tunnel is particularly well known. It is a two-lane paved road (39° 9'50.83"N 125°59'26.98"E) that dives beneath the Taedong River near the Kangdong Palace and then reemerges a kilometer away. It is surmised that there is another tunnel that pulls off from the main one and connects to other elite areas in the region.

Another part of the network uses the country's railways. The Obong-ri Elite Train Station (40°18'18.13"N 125°12'18.72"E) is positioned in a mountainous region north of Kusong. The entire complex encompasses roughly 17 sq. km and contains two train stations, housing for personnel, various support structures and it has two rail lines that go into a hill and disappear. It is not known if this is simply an underground train repair center or if the lines continue underground and could carry Kim Jong-un many kilometers away on his armored train without anyone knowing.

I would like to thank my current Patreon supporters: Amanda O., GreatPoppo, Joel Parish, John Pike, Kbechs87, Russ Johnson, and ZS. 

--Jacob Bogle, 6/5/2022

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What Lies Beneath the Underground Republic

The internal workings of North Korea largely remain a secret to many in the world, and even Western intelligence agencies have bemoaned the relatively sparse amounts of information that flow out from the DPRK's borders. It's even suspected that the United States has no more than two or three low-level spies in the country - if there are any at all. This means that one of the main sources of information about this "hermit kingdom" comes from what can be gleaned through a vast array of satellites. 

One thing that becomes clear from these spies in the sky, is that North Korea has a fetish for digging.

During the Korean War, Kim Il Sung and his army witnessed the terrible and far-reaching ability of the Allied air forces to knock out military and economic targets from the sky. The northern part of the Korean Peninsula had been turned into Korea's industrial and most developed region by Japan during their 35 year occupation, but by the end of the three year Korean War, upwards of 85% of all buildings in North Korea had been completely or partially destroyed. The Korean War saw more tonnage of bombs dropped than in the whole of the Pacific Theater of WWII.

Kim Il Sung's expectation that Korean War II was imminent, and based on the lessons he learned during the first war, led to him commanding that the whole country be fortified, saying in 1963, "we must dig ourselves into the ground to protect ourselves". 

The practical results of this are the countless miles of trenches along nearly every hill, a coastline ringed with artillery positions and anti-invasion obstacles, the second largest combined military and paramilitary force in the world, and lots and lots of tunnels, bunkers, underground factories, and other sites constructed beneath the surface and out of view. 


At this point, I want to sound a note of caution to those who like to let stories of North Korean mysteries run away with them. There has been plenty of speculation about the true extent of North Korea's underground infrastructure, with some going so far as to claim that most of their military bases are actually buried beneath the ground. The truth is, while both small and vast underground sites exist across the country, commercial satellite images do not support the idea that there's basically a parallel country underground. 

Military sites are easy to find if one knows what to look for and reviewing current and historic satellite images only reveal underground sites at some of them, and most of those are relatively small.  The only way you could claim that most bases have an underground facility (UGF) is if you include small storage bunkers or gun emplacements that are situated a few meters into a hillside. But I don't accept the definition of an "underground facility" as merely being "any usable structure with an inch of dirt on top". For the purposes of this article, UGFs are a sizable structure built into the ground, where the rock cover would provide meaningful protection from bombs and missiles.

Aside from military sites, major factories with UGFs are likewise easy to spot. I have looked at every square meter of the country more than once, and the 2021 AccessDPRK Pro Map is swollen with over 13,000 distinct military-related sites plus dozens of factories with an underground component. However, to reiterate, I haven't seen anything in commercial satellite imagery that convinces me there is a nationwide system of connected tunnels and underground sites.

Based on the AccessDPRK 2021 Map, Pro Version, the country has over 1,500 identifiable tunnels and underground facilities.

The sheer number of these sites overall is a little mind-boggling when you consider how relatively small North Korea is. The above map shows each of the 1,500+ tunnels and important underground facilities that I have managed to locate, as well as coastal batteries that have a clear underground component. It doesn't show the 850 hardened artillery sites, 492 drive-thru bunkers, or other installations that only have small access tunnels. The total number of large and small UGFs (which includes artillery sites and small storage areas) is estimated to reach as high as 14,000. 

Some sites were clearly constructed decades ago and were either abandoned or serve as emergency facilities in the event of open warfare. Because of this, their entrances have become overgrown with vegetation and that can make identification difficult. Furthermore, others have indeed been abandoned and mining operations or other domestic activities have encroached on the site; I saw little need to map those. 

There are also scores of stories about secret underground escape routes that connect Pyongyang and major palaces with underground rail lines that would allow the Kim family and top officials to be spirited away to the far north of the country, and even to China.

According to a 2015 report, the US military has mapped 6,000 to 8,000 of these "VIP" underground sites that North Korea's leadership could use to either hide or escape the country. The vast majority of them, however, would be simple bomb shelters (something that is common in South Korea, too). And, while this report lends credence to the idea of large, interconnected networks of underground facilities, the problem is that there is almost no direct visible evidence in the public sphere for such a massive system (although smaller tunnel segments have been identified). Additionally, this system is for the country's top leadership and isn't part of the normal domestic and military infrastructure of the country. So, this article is only going to focus on other underground infrastructure that plays a more "daily role" in the country.

While the exact purpose of each and every one of the sites is impossible to ascertain by simply looking at them from the air, most tend to fall into a handful of categories. There are a few major underground facilities, such as the Punggye-ri Nuclear Site, the Panghyon underground aircraft factory, and Kim's hardened helicopter base (which is part of a much larger underground command and control base). Most of the others can be classified into these: the underground factory or laboratory, the unspecified underground facility (many with protective berms at tunnel entrances), underground facilities at Navy and Air Force bases (excluding HARTS and storage bunkers), and basic tunnels (either individual tunnels or usually in groups of three).

The following set of images shows examples of various types of underground facilities. The satellite images used cover a large range of dates, but they were chosen because they best showed the sites in question.

Click on any image for an enlarged view.

The Hagap Facility in Chagang Province (40.081644° 126.189346°) is an example of a major underground site. Its exact purpose is unknown, but the two main theories are that it's either part of North Korea's nuclear program or a secured storage site for important government archives. Construction of the site has been ongoing for decades, punctuated by periods of inactivity, but since 2016, work has been steady.

Ryoho-ri Underground Naval Base (39.876051° 127.785328°)

This is a submarine base and the headquarters for the East Sea Fleet. It is one of 13 naval bases that have an underground or hardened facility. Ryoho-ri has two underground entrance points and suggests the existence of a large underground facility at least 300 meters in length and that could likely extend a further 150 meters into the hill. 

Ryoho-ri is so important that Kim Jong Il had a villa built nearby and both the villa and base have special rail access.

Pukchang Airbase (39.512137° 125.958563°)

Pukchang is one of 22 airbases and heliports that have associated underground facilities. I've already written about two of these in detail, the Sanghung-dong VIP Heliport in Pyongyang and the Kangda-ri Airbase near Wonsan. 

Pukchang is home to a Mig-23 fighter wing and has three main underground entrances into Obong Hill. It is also adjacent to the Yonggang-ni Helibase which has its own small UGF. 

Such facilities are used to store important aircraft and equipment, conduct maintenance, and at some airbases, even engage in manufacturing parts.

Tonghungsan Machine Plant (39.953611° 127.546918°)

Located in Hamhung, this is a major underground factory and is associated with North Korea's arms industry. Beginning in 2016, major reconstruction work began on both the underground portion and the external buildings. This reconstruction kicked off a series of new building and renovation projects at multiple arms facilities around the city including the Chemical Materials Institute and at the Hungnam Fertilizer Plant which produces chemicals used in various programs. 

Depending on Tonghungsan's exact size and layout, parts of the factory could be protected by over 150 meters of rock.

Taedonggang UGF near Pyongyang (39.174538° 125.946416°)

This is underground facility has a publicly unverified purpose. Located 6.5 km across from the Kangdong Residence on the other side of the Taedong River, it consists of four entrances divided into two sections. Tunnels 1 and 2 appear to be more for underground storage, while the size and configuration of the road and tunnels 3 and 4 suggest that they're for larger equipment (possibly TELs and MRLs).

Based on rough calculations of the volume of the spoil piles, there is at least 40,000 cubic meters of interior space for tunnels 3 and 4. That's the equivalent of a room 63x63 meters in size with 10-meter-high ceilings. The existence of a gantry crane and dedicated electrical substation can also clue us in to what purposes the site may be used for.

Pyongyang Armed Forces District UGF (39.059308° 125.733921°)

One of the largest identified underground facilities is beneath a hill in the middle of Pyongyang. One of the oldest entrance points is located at 39.059308° 125.733921° and is next to a secured villa. The tunnel can take VIPs into the facility that occupies a large portion of the hill or across the hill to the Sanghung-dong Heliport, where six helicopter hangars are protected by steel blast doors and hardened walls. 

Roughly 660 meters northeast from the original entry point is the newest entrance. It was added in 2017 and can take important people from an assembly hall directly into the UGF. 

This Armed Forces District UGF is one of multiple hardened command and control facilities within the city. 

While North Korea's engineers are capable of constructing large underground factories, they're still limited by the technology, education, and other factors that they have access to. North Korea is well known for their "speed campaigns" and for constructing large projects rapidly. Lack of enough materials due to sanctions and additional factors means that some of these projects end up shoddily built, with problems arising often and even occasional building collapses. These failures can also extend to military sites.

The following site is a coastal artillery position in North Hamgyong Province (41.896007° 129.950076°) that suffered a collapse, largely destroying the site.

Area before the collapse.

Area after the collapse.

North Korea built one of the deepest subway systems in the world, and they have a history of building underground facilities not only within their own borders but also around the globe. 

These places aren't just for hiding weapons or keeping the Kim family safe. Four massive tunnels that traversed the DMZ into South Korea are known about and some estimate that fifteen to twenty others could exist. Such infiltration tunnels could enable an invasion into South Korea with tens of thousands of soldiers and vast sums of equipment without warning.

From infiltration tunnels to escape routes 100 meters underground to new UGFs at ballistic missile bases, the difficulties in discovering this underground infrastructure and combating its ability to hide people and weapons present a continuing obstacle to intelligence. It may also provide a potentially unacceptable level of uncertainty regarding any offensive strike against the country by the United States or South Korea, as they may not know where each target person is exactly or if every nuclear bomb or technological site was hit. 


I would like to thank my current Patreon supporters: Amanda O., Anders O., GreatPoppo, Joel Parish, John Pike, Kbechs87, Planefag, and Russ Johnson.

--Jacob Bogle, 2/17/2021

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