The U.S. military has been here before: fighting an enemy who wears no uniform, one who hits and runs then disappears, blending in with local villagers. It has pursued before, with overwhelming technological superiority, guerrilla fighters who improvise weapons and use the terrain to hide. The rugged mountains along the Afghanistan-Pakistan frontier, where the Taliban and al Qaeda hide, are as effective at concealment as the dense swamps and forests of Vietnam, Laos, and Cambodia. In Vietnam, the U.S. military learned that when striking an elusive enemy, high-performance jet fighters were much more successful when they were directed by lighter,...