The late Col. Townsend Whelen, who probably knew as much about living in truly wild country as anyone, carried two knives, neither of which would have interested John Rambo. One was a Marble's hunter with a 31/2-inch blade, which the colonel carried in a homemade sheath. The other was a smallish three-bladed folding knife of the pattern we call the "stockman." So skillful was Whelen in the ways of the wilderness that he never had to "survive," but for the rest of us, a truly heavy-duty knife often comes in handy, if only to do something mundane like build a blind. And if you have to combat a mountain lion in close quarters, or amputate your own hand when it gets trapped under a boulder, or build a temporary shelter when you get lost, a big knife will do better than a small one. Here are five very good ones. I've used them all and can testify to their effectiveness.