page_title: Haean
section_title: Fourth tunnel
hierarchical_section_title: Haean / History / Fourth tunnel
caption_attribution_description: English: A West German engineer inspects a tunnel boring machine inside a South Korean counter-tunnel constructed to eliminate the value of North Korean tunnel No. 4 by intersecting it. Both tunnels are located near Kach'il-Bong Peak.
context_page_description: Haean is a township in Yanggu County, Gangwon-do, South Korea. Haean sits in the distinctive Haean Basin, which was nicknamed The Punchbowl by UN forces during the Korean War. The northern part of the basin lies within the Demilitarized Zone, and the area saw heavy fighting during the war.
context_section_description: The fourth "tunnel of aggression" was discovered on March 3, 1990, in the northern part of Haean Myeon, which borders North Korean territory.
  
  It is a deep tunnel dug from the northern side within the demilitarized zone, passing under the armistice line.  Three similar tunnels were found between 1974 and 1978, all farther west and closer to the South Korean capital, Seoul.  The tunnel was found at a depth of 145 m and was explored through a borehole and a countertunnel, since the tunnel was incomplete and did not yet have an entrance on the southern side.
  
  The tunnel is estimated to be over a mile long and to extend at least 4000 feet on the southern side of the demarcation line.
  
  South Korea alleged that the North Korean military dug the tunnel in preparation for an invasion of the South, violating the terms of the cease-fire agreement of 1953.
caption: Digging in 1990 of the countertunnel to join the incomplete tunnel
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