There were many entrances to the tunnels. A fighter could pop up, make a quick surprise attack, and disappear before a reaction. At first the Americans were baffled, but they quickly discovered the tunnels and had to invent a new method of warfare to combat. Because of the size of the tunnels and openings, only the smallest soldiers could go in. Most tunnels were booby-trapped, or often had VC waiting below. It was extremely dangerous, and the tunnel rats became famous as dangerous, hard fighting men.