Kim Hah-chul were killed in the tunnel by a North Korean explosive device. The blast also wounded five Americans and one South Korean from the United Nations Command.

The tunnel, which was about 3 by 4 ft, extended more than 1 km beyond the MDL into South Korea. The tunnel was reinforced with concrete slabs and had electric power and lighting. There were weapon storage areas and sleeping areas. A narrow-gauge railway with carts had also been installed. Estimates based on the tunnel's size