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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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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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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North Korea's Underground Navy: A Review

Many countries have underground facilities for their navies. Places to protect submarines, places to defend against surprise or nuclear attacks, underground storage, places that have all kinds of purposes.

One large example was the Soviet base in Balaklava, Crimea. China currently maintains at least six underground submarine bases. The United States has an enormous underground fuel storage site in Hawaii.

North Korea is no different.

North Korea has a tremendous amount of experience digging tunnels. I have found hundreds of tunnels across the country, hundreds of artillery sites that pop out of tunnels, scores of underground factories, and quite a few underground naval sites.

Bounded on two sides by the ocean and with 2,495 km of coastline, the Korean People's Navy has a strength of 60,000 men and over 800 vessels, making it one of the largest navies in the world in terms of vessel numbers. And while most of their naval technologies are decades behind the West, Kim Jong Un has been focusing on modernizing the fleet. Furthermore, what they lack in technology they can make up (some of that gap) by sheer numbers.

North Korea has 70-80 submarines, which places them on par with the United States (based on numbers) and far outpaces South Korea. Their navy has been able to inflict substantial damage in attacks like the Second Battle of Yeonpyeong in 2002.

And so, it makes sense to marry navy and tunnel together. Underground naval bases provide safety in the event of attack and secrecy to develop, arm, refuel, and launch attacks. Having multiple sites also makes it more difficult for an attacking country to quickly knock out North Korea's navy.

The country has 13 identified underground naval sites. Some can accommodate submarines but most currently serve various types of surface ships. Interestingly, North Korea's main submarine base for the Sea of Japan (East Sea), which is based on Mayang Island, lacks any apparent underground facilities.

(Click on images for larger view)

The facilities range from simple tunnels to more complex facilities that are accessed from the sea and cover a large footprint.

Starting with the Yellow Sea (West Sea) bases:

Taewha-do Underground Base: 39°25'59.69"N 124°37'2.39"E

Taewha-do is on an island (the -do suffix means island) and consists of a small underground facility and a turntable to enable vessels to be moved around the base on a short rail system. There is only a single dual entrance/exit point to the underground facility (UGF) but the island's size could theoretically accommodate an enormous UGF inside. However, it only appears to house small patrol boats and the island garrison is no larger than battalion sized.

Very little information about the base is publicly available and most of the information that does exist relates to a series of small military actions during the Korean War, before the UGF was construction. The island rises steeply out of the ocean and can provide up to 600 feet of solid rock on top of the UGF, giving it excellent protection.

Sok-do is not necessarily an underground base but rather it is a set of four hardened pens that allow craft to be protected. Located at 38°38'7.33"N 125° 0'26.27"E, it doesn't appear to be in use. It lies just 5 km from Pip'a-got, which is a primary naval base.

Pip'a-got is the largest naval base immediately outside of the West Sea Barrage, which cuts off direct access to the Taedong River and Pyongyang.

Pip'a-got naval base.

The base consists of a large protected harbor (created by a set of breakwaters), hundreds of buildings, and seven distinct ship handling sites (dry docks, main harbor, UGF, etc). It covers approx. 5 square kilometers.

The underground component consists of a 600-meter long tunnel that connects a turntable (that can take ships from a slip and bring them to the tunnel entrance) to an exit that enters directly into the sea, bypassing the large seawalls.

The tunnel could include other facilities like fueling, loading weapons, and repair, but the interior layout is not known. The hill it cuts beneath rises from ~90 feet at the turntable to a maximum height of ~250 feet along the path of the tunnel.

Sunwi-do & Sagot (Ryongho) Bases
Sunwi-do has a small base at the far northeast end of the island. It is across from the larger Sagot base on Ryongho Island 4 km to the north. Both bases are in South Hwanghae Province are the southernmost underground naval facilities on the west coast. The base at Sunwi-do lies a 31 km from the South Korean island of Yeongpyeong.

The base on Sunwi Island, 37°46'11.59"N 125°20'21.45"E

At its height, the island provides ~180 feet of rock over the Sunwi tunnel which runs for 250 meters.
North Korea has several classes of patrol boats and Sunwi seems to be a base for them. In the imagery provided by Google Earth, at no time has there been more than 13 ships and none over ~28 meters in length.

In this image of Ryongho, four classes of ship can be seen. Upwards of 36 ships have been seen at Ryongho but some may have actually been small fishing vessels along with the military craft.

Sagot base is split between two main facilities. One is at the town of Sagot, on the mainland 1.8 km to the north, and the second is the UGF on Ryongho Island (37°48'17.24"N 125°21'9.58"E).
A direct line from the Ryongho entrance to the exit runs 290 meters but the full tunnel path isn't a straight line. It is likely at least 365 meters in total length. Between 150 and 250 feet of rock sits above the site, depending on location.

The exit has apparently silted up and cannot be used as a direct exit point for sailing into the sea. Any vessel must be towed down the "hump" from the UGF exit point to the water. Why this hasn't been corrected would only be speculation, but it has been the case since at least 2004.

NK-01 antiship cruise missiles (a local variant of the Soviet P-15 Termit (aka Styx) are believed to be deployed at the base.

Along the northeast edge of the island is a series of small tunnels for terrestrial vehicles and other equipment. This is a common feature found at many bases across the country.

East Sea (Sea of Japan) Bases

Puam-dong is the first base on the east coast. (Going north to south, as I did for the Yellow Sea bases.) Located at 41°19'17.15"N 129°46'4.71"E it is a primary navy base and has a large harbor protected by ~470 meters of breakwaters.

The base has been called a submarine base (and some of its features support that conclusion) but no submarines are visible in the available imagery. Other vessels stationed at the base include the Sohung-class PTG (guided missile patrol boat). This has been a key base for them since at least the 1980s.

Puam-dong is divided into two sections because of a hill in the middle of the base. The main section has headquarter facilities, barracks, and other buildings. The second section (to the south) is for maintenance.

The tunnel runs for at least 425 meters and the hill provides ~270 feet of rock above. The base also has a small underground storage facility higher in the hills at 41°20'12.02"N 129°45'24.94"E.

Cha'ho is a major submarine base located at 40°12'18.28"N 128°38'59.31"E in S. Hamgyong province. Including the harbor, it covers approx. 7.7 square kilometers.

Development of Cha-ho began in 1961 and it was transformed from a small base for patrol craft to a major submarine facility. By 1968 the underground portion was under construction. Unlike many other bases, it has rail access.

Unlike land-based underground facilities, where large piles of debris can be seen and analyzed to yield the approximate volume of the UGF, sea-based sites tend to lack any visible debris (since it can just be dumped under water) making it almost impossible to determine its size or layout using traditional methods. (Technology does exist that can shed light on the internal nature of the site using special techniques, but those are beyond the reach of most.)

However, at least a portion of the quay positioned between the entrances of the UGF may be made up of excavated debris based on a review of declassified images.

Taking the curved shape into account, the tunnel runs at least 330 meters and is protected by upwards of 200 feet of rock. I suspect that the main tunnel is placed farther back than I have it drawn, but that's why things are labeled "approximate".

Throughout the base Sang-O class (mini subs) and Romeo-class submarines can be seen. Romeo's are Chinese built, Soviet originated submarines that North Korea first acquired in 1973.

Ryoho-ri (Toejo-dong) Base is the location of the East Sea Fleet Command. It goes by several designations, Ryoho-ri, Yŏho-ri (an alternate spelling), and Toejo-dong (the name of the bay and also commonly used). Its location is 39°52'33.92"N 127°46'43.45"E.

As if signifying the base's importance, one of North Korea's many leadership residences is adjacent to the base. Ryoho is also serviced by rail.

The base doesn't appear to have any shipbuilding capabilities, but it does have a small repair facility for patrol boats. As mentioned, it is the headquarters for the East Sea Fleet and commands all of the bases and associated facilities along the east coast. One of the subordinate units at the base is KPA Unit 158.

The underground facility follows the same basic design as all the others. Its tunnel is ~315 meters long and is covered by roughly 200 feet of rock.

Samil-ri is a small UGF that consists of a single entry point. Located at 39°22'18.03"N 127°26'18.43"E it is on a small peninsula that's part of the much larger Munchon Naval Base.

Across from it on the other side of the peninsula (over 900 meters away) is a turntable but it doesn't appear to have been used in years and the images available on Google Earth make it difficult to confidently assert that there's a tunnel connecting the two points.

It's hard to gauge how active this site is, particularly since the turntable doesn't appear to be in use, but the wider Munchon area has been the focus of a large modernization and expansion program which has been ongoing since 2014. The Munchon-Wonsan region is an important military and industrial area, and various improvement projects have occurred there including the Kalma International Airport, Wonsan-Kalma tourist zone, and the nearby Hodo missile test facility.

Of note, various materials can be seen at the entrance site in recent images that could be used in a restoration project.

Sindo & Yodo island bases

Sindo is a small, narrow island in Yonghung Bay, off of Wonsan. It has a small underground site but unlike Samil-ri it definitely doesn't have an exit point. It is located at 39°13'18.11"N 127°31'10.04"E and would have a maximum length of 85 meters (based on the particulars of the island). The island's garrison seems to be geared toward operating coastal defense artillery and is located nearly a kilometer to the east.

The Yodo island site is located 8.7 km east of the Sindo site. Like Sindo, it doesn't have a second entry/exit point, but it does have a turntable. This allows approx. 8 vessels to sit on the beach and then individually brought into the tunnel for servicing and then moved back out and onto the "holding yard".

If you look closely at the image, you can see a vessel halfway in (or out) of the tunnel entrance.

Yodo has a much larger garrison and even has a small grass runway that extends for 660 meters (although a dirt path cuts across it near the southern end). The naval tunnel may run for 180 meters into the hill to reach 140-150 feet of rock depth. Directly across is a hardened coastal artillery battery and those tend to have small tunnels connecting them to the outside. If we assume the tunnel comes close to the battery, then the tunnel may run as much as 200-230 meters.

Namae Navy Base

Located at 38°48'9.76"N 128° 8'18.58"E Namae is a large navy base with a breakwater that creates 38 hectares of protected harbor. The northern end of the base contains the underground facility. Namae has the facilities available to service all of North Korea's surface fleet and may be able to dock submarines.

The entrance is approx. 20 meters in width and could be covered by as much as 200 feet of rock. There does appear to have been an exit point built, but the tunneling work was either never finished or there was some other problem. An exit structure was built but is in a state of disrepair.

By 2013 a hole had appeared in the roof of the possible exit structure and by 2019 the roof had collapsed entirely. Had the entire facility been completed, the tunnel would have run 515 meters and would make it the second longest confirmed tunnel after Pip'a-got.

Possible exit structure with collapsed roof.

The last of North Korea's underground navy sites is at Changjon, 38°43'59.96"N 128°12'45.45"E.

It's the southernmost naval facility on the east coast and lies a mere 18 km from the military demarcation line.

Changjon is divided into two sections. The northern section contains a large active navy base, the southern section (~1.8 km away) has the underground facility but it appears to have been abandoned. No military vessels can be seen in Google Earth images (which go back to 2005), and there is a civilian dock with a floating restaurant just a kilometer away. It's part of the Kumgang tourism system.

At the same time, a small naval unit is still directly connected to it and the base did serve as a "frontline base for North Korean submarines" before being suspended as part of the creation of the aforementioned tourist zone. However, Kim Jong Un has recently expressed a desire to enlarge the base, so this portion of it may become active again in the future.


Additional reading:
Work on Major Hovercraft Base Advances, AccessDPRK, 1/17/2020


I would like to thank my current Patreon supporters: Amanda O., GreatPoppo, Kbechs87, Planefag, Russ Johnson, and Travis Murdock.

--Jacob Bogle, 5/9/2020
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