by Kyle Mizokami
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.
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http://nationalinterest.org/blog/the-buzz/north-koreas-secret-strategy-war-america-go-underground-20525
