Only 44 kilometers from Seoul (less than an hour's drive), the third tunnel was discovered in October 1978. Almost identical in structure to Tunnel 2, the 1.635 kilometer-long tunnel is 1.95 meters high and 2.1 meters wide. It penetrates 435 meters south of the Military Demarcation Line at a point 4 kilometers south of Panmunjeom, running through bedrock at a depth of about 73 meters below ground. Capable of moving a full division (plus their weapons) per hour, it was evidently designed for a surprise attack on Seoul. This tunnel is only 2 kilometers from a key outpost defending the Munsan corridor leading to Seoul.