Incursion tunnels under the DMZ

http://en.wikipedia.org/wiki/Korean_Demilitarized_Zone#Incursion_tunnels

Incursion tunnels

Soldiers from the United Nations Command on observational operations in South Korea. (Circa1997).Starting on November 15, 1974, the South discovered four tunnels leading under the DMZ. The first of the tunnels was discovered by a South Korean Army patrol, noticing steam rising from the ground. The initial discovery was met with machine gun fire from North Korean soldiers. Five days later, during a subsequent exploration of this tunnel, U.S. Navy Commander Robert M. Ballinger and ROK Marine Corps Major Kim Hah Chul were killed in an explosion triggered from North Korea, along with the wounding of six additional United Nations Command personnel, five American and one South Korean. This first tunnel was about 3 by 4 feet (0.9 m × 1.2 m) and extended over 1,000 meters (3,300 ft) beyond the Military Demarcation Line (MDL). When the first tunnel was discovered, it was reinforced with concrete slabs, electric power and lighting, weapons storage and sleeping areas and had a narrow gauge railway with carts, capable of allowing approximately 2,000 soldiers per hour to traverse it. The second was discovered on March 19, 1975, of similar length, between 50 and 160 meters (160 and 520 ft) below ground, but was larger than the first, approximately 2 by 2 meters (6.6 ft × 6.6 ft). The third tunnel was discovered on October 17, 1978. Unlike the previous two, the third tunnel was discovered following a tip off from a North Korean defector. This tunnel is about 1,600 meters (5,200 ft) long and about 150 meters (490 ft) below ground. A fourth tunnel was discovered on March 3, 1990. It is almost identical in structure to the second and the third tunnels.[10]

The tunnels were dug by North Korea and are presumed for use by the military as an invasion route. Each tunnel is large enough to permit the passage of an entire division of infantry in one hour. Due to its narrow build, neither tanks nor any other vehicle can pass the tunnel. All the tunnels run in a north-south direction and do not branch off. The planning for the tunnels got progressively more advanced (for example, the third tunnel slopes upward slightly as it progresses southward, so that water does not stagnate). The orientation of the blasting lines within each one indicates that North Korea dug the tunnels. Upon their discovery, the North claimed that they were for coal mining; however, no coal can be found in the tunnels, which are dug through granite, but some of the tunnel walls were at some point painted black to give the appearance of coal.

Today, it is possible to visit some of the tunnels as part of guided tours from the South. Some of the famous tunnel tours include the Third Tunnel of Aggression which was discovered in the 1970s.


So, WI any of these Incursion Tunnels had been used by the NKs to invade ROK before they were discovered at any time between 1974 to 1990 ?
 
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