On November 15, 1974, an Army reconnaissance team from the 25th Division patrolled the Demilitarized Zone (DMZ) in Yeoncheon County, Gyeonggi Province, when they noticed steam rising from the ground. They began digging into the suspicious area and uncovered the entrance to a tunnel that North Korea had secretly excavated.
A secret underground passageway, measuring 3.5 kilometers (about 2.17 miles) in length, 90 centimeters (roughly 2.95 feet) in width, and 1.2 meters (approximately 3.93 feet) in height, was discovered 2.5 to 4.5 meters (about 8.2 to 14.7 feet) beneath the surface. Military analysts believe it was designed to support a potential invasion, capable of channeling a regiment-sized force into Seoul within an hour. The tunnel directly threatened the nation’s heart, located just 65 kilometers (about 40 miles) from the South Korean capital.
The unearthing of this first tunnel shattered the illusion of inter-Korean peace, revealing North Korea’s aggressive intentions and serving as a wake-up call for security forces on the peninsula. The discovery exposed the possibility of an underground invasion, underscoring the urgent need for heightened vigilance and enhanced surveillance measures.
Following the unsettling find, South Korean and U.S. forces increased their surveillance efforts to locate additional infiltration routes. Their persistence led to the detection of three more tunnels: the second in March 1975 near Cheorwon, Gangwon Province; the third in January 1978 near Panmunjom; and the fourth in March 1990 in Yanggu County, Gangwon Province.
The military employed advanced detection tools to locate these hidden passages, including ground-penetrating radar, seismic sensors, and specially trained K-9 units. Each tunnel was oriented towards Seoul, proving North Korea’s ongoing invasion preparations. These discoveries posed a serious security threat and dealt a severe blow to inter-Korean relations and efforts at trust-building.
After exposing the first tunnel, North Korea denied any involvement, dismissing the discovery as a South Korean fabrication. Pyongyang accused Seoul of manufacturing the tunnel incident to sabotage inter-Korean relations. However, the international community was not persuaded. The United Nations Security Council passed a resolution condemning North Korea’s covert tunnel construction, with many nations joining in to denounce Pyongyang’s provocative actions.