North Korea, one of the most secretive countries in the world, is no stranger to building underground military facilities. Whether a tunnel dug under the demilitarized zone designed to pass thousands of troops an hour, or bunkers to accommodate the regime’s leadership, North Korea has built extensive underground facilities designed to give it an edge in wartime.
One of the earliest examples of North Korean underground engineering was the discovery of several tunnels leading from North Korea under the demilitarized zone to South Korea.
The first tunnel was located in 1974, extending one kilometer south of the DMZ. The tunnel was large enough to move up to two thousand troops per hour under the DMZ. A U.S. Navy officer and South Korean Marine corporal were killed by a booby trap while investigating the tunnel.
Thanks to a tip from a North Korean defector, an even larger tunnel was discovered in 1978, a mile long and nearly seven feet wide.
Since then at least four tunnels have been discovered, with reinforced concrete slabs, electricity for lighting and fresh air generation, and narrow railway gauges to shuttle dirt and rock back to the tunnel entrance.
Collectively, the four tunnels would have likely been able to move a brigade’s worth of troops an hour under South Korea’s defenses.
If it has passed, it may be because North Korea has decided to tunnel in different ways.
The North Korean People’s Liberation Army Air Force is believed to have three different underground air bases at Wonsan, Jangjin and Onchun.
The underground base at Wonsan reportedly includes a runway 5,900 feet long and ninety feet wide that passes through a mountain.
According to a defector, during wartime NK PLAAF aircraft, including MiG-29 fighters and Su-25 Frogfoot ground-attack aircraft, would take off from conventional air bases but return to underground air bases. This is plausible, as one would expect North Korean air bases to be quickly destroyed during wartime.
Another underground development is a series of troop bunkers near the DMZ.
A North Korean defector disclosed that, starting in 2004, North Korea began building bunkers capable of concealing between 1,500 and two thousand fully armed combat troops near the border.
At least eight hundred bunkers were built, not including decoys, meant to conceal units such as light-infantry brigades and keep them rested until the start of an invasion.
Other underground facilities are believed to have been constructed to shelter the North’s leadership.
According to a South Korean military journal, the United States believes there are between six thousand and eight thousand such shelters scattered across the country.
This information was reportedly gathered from defectors in order to hunt down regime members in the event of war or government collapse.
North Korea is believed to have hundreds of artillery-concealing caves just north of the DMZ.
Known as Hardened Artillery Sites, or HARTS, these are usually tunneled into the sides of mountains.
An artillery piece, such as a 170-millimeter Koksan gun or 240-millimeter multiple-launch rocket system, can fire from the mouth of the cave and then withdraw into the safety of the mountain to reload.
These sites are used to provide artillery support for an invasion of South Korea or direct fire against Seoul itself. As of 1986, and estimated two hundred to five hundred HARTS were thought to exist.
According to a report by the Nautilus Institute, North Korea is also thought to have “radar sites in elevator shafts that can be raised up like a submarine periscope; submarine and missile patrol boat bases in tunnels hewn in rock; tunnels a kilometer or more in length for storing vehicles and supplies, or to hide the population of a nearby city.”
THESE pictures reveal the inside of invasion tunnels dug by North Korea – which Kim Jong-un could use to send as many as 30,000 troops an hour to the South in a stealth attack.
Fears have been raised that as many as 84 secret war tunnels have been built, with some boasting sleeping areas, a railway and enough space to move tanks.
The existence of these sprawling tunnels has raised the risk of a surprise invasion amid heightened tensions between the North and South.
The first major tunnel, which stretches 3.5km in length, was discovered in November 1974.
It was found north-east of Korangpo in the Korean Demilitarized Zone (DMZ), extending 1km past the official border.
The walls, which are 1.2m high and 1m wide, are reinforced with concrete slabs.
The tunnel has the capacity to move one regiment an hour – which means between 10,000 and 30,000 elite soldiers could pour through the cramped space.
It was equipped with a narrow-gauge railway and rail cars and was lit with lamps connected to 220-volt power lines.
A second tunnel was found in March 1975, 13km north of Chorwon, which stretched 1.1km south of the heavily-fortified border.
Twice as wide as the first tunnel, it is large enough to send through heavy weapons, tanks and field artillery.
Troops would be able to march through the underground tunnel at three to four abreast – meaning thousands could be deployed in an hour.
The second tunnel ran for 3.5km at a depth of 160m and is it understood to be 2.2m wide.
A third tunnel was uncovered after a tip-off from North Korea defector Kim Bu-seong on 17 October 1978.
It runs for 1.6km, some 73m below the surface, just south of Panmunjeom.
After it was built, coal dust was smeared around the entrance so it would be disguised as an abandoned coal mine.
It is now blocked by three concrete walls – but it still has enough room to transport 30,000 troops per hour.
Another tunnel was discovered in March 1990 which runs for 1,052m.
The Daily Star reported that the South Korean government believes there could be 16 more undiscovered tunnels.
A retired South Korean general has previously claimed there were as many as 84 tunnels beneath the border.
But the South dismissed the claims made by Hahn Sung-chu, a former two-star general, saying they were “groundless”.