Between the 1960s-1980s, North Korea dug tunnels under the Demilitarized Zone (DMZ) in an attempt to conduct a surprise invasion of South Korea from underground.
The first tunnel was discovered in 1974 by a South Korean Army patrol that witnessed steam rising from the ground and heard underground explosions. Based on intelligence reports, Republic of Korea (ROK) forces searched for more suspected tunnels in the area around Cholwon, near the center of the DMZ, hiring a Korean mineral firm to conduct the drilling. However, after sixty-nine boreholes, no additional tunnels were found.
In late 1974, knowing of the U.S. Army Corps of Engineers (USACE) Far East District’s (FED) expertise in high-precision drilling for water wells, the ROK made a formal request for the District’s assistance.
Since 1965, FED has employed a drilling program for water wells on U.S. military installations across Korea.
Following the request for assistance, the District began preparations to drill near the DMZ. By March 1975, FED established a Precision Borehole Drilling Unit and dispatched drill crews to the DMZ. The teams worked in three shifts; eight hours each, twenty-four hours a day.
After twelve days of intensive drilling, 155 feet below the ground, one of the drills hit a void.
The District had discovered a second tunnel. The passage was 4 feet high by 3 feet wide and could have accommodated up to 30,000 troops an hour.
Following the discovery of the second tunnel, Eighth Army established a Tunnel Neutralization
Team (TNT) that FED assisted through technical and logistical support.
“The FED drilling teams worked along the entire length of the DMZ to locate additional tunnels,” said Kim Se-kon, who participated in the DMZ Tunnel Neutralization Team (TNT) drilling as a senior geologist for FED.
At the time, a North Korean defector reported that there was a tunnel in the DMZ, after which excavation work was carried out near the Armistice village of Panmunjom.
“It was hard to locate the exact point since the point looking from the north was different from the point looking from the south. But by chance, on June 10, 1978, an explosion was detected in an old abandoned borehole, from what was apparently a faulty dynamite charge planted years earlier. Immediately, the FED drilling team carried out reverse tunnel excavation work in the surrounding area, and on October 17, the 3rd tunnel was discovered 15 meters ahead of the tunnel end where the team was previously working.”
The tunnel was located 2 kilometers from the United Nations Forces Forward Base, which supported the Military Armistice Commission in the Joint Security Area at Panmunjom. Furthermore, it was the closest tunnel to Seoul out of all the North Korean tunnels in history. This fact caused significant shock and uproar at the time of discovery.
According to Kim, about 10 FED employees received commendations from the ROK Minister of Defense for their discovery of the tunnel. The District continued to support tunnel neutralization efforts until the 1990s, when the ROK took over the activity entirely.
Kim majored in geology at Yonsei University and began working for FED in 1977. He retired in 2017 after 40 years of service.
“I just did what I had to do, and I am honored to be involved in such meaningful work. It was a long time ago, so there are not many records left, and it is being forgotten, but I want people to remember that the FED employees made a great contribution to the discovery of the tunnels,” said Kim.
Tunnel detection near the DMZ, a monumental task by any measure, remains one of the District’s more distinctive accomplishments, reflecting the expertise and professionalism of the Far East District and its workforce.