North Korea even created underground shelters for artillery. During bombing artillery was rolled into bunkers located inside mountains. When a lull came the guns were rolled back out onto a firing area, fired some shells, and rolled back into the bunker again. Unlike other examples of underground warfare North Korean troops did not just remain in the tunnels. North Korean forces were sheltering in the tunnels from the bombing and shelling and awaiting US bayonet attack. When US forces reached the ground in the area of the tunnels, chosen North Korean units would emerge to engage in hand-to-hand combat taking advantage of their numerical superiority.