The United States could use a force of intercontinental ballistic missiles with conventional warheads because nuclear weapons may not deter terrorists and rogue states, the general in charge of the U.S. Strategic Command says. Marine Corps Gen. James E. Cartwright told a Pentagon-sponsored missile defense conference on Monday that "it's very difficult for a nuclear weapon to be a credible deterrent against an extremist." In addition to the "tyranny of distance" that makes it hard for military forces to get to an area of the world very quickly, there is also the problem of the inadequate speed of current conventional...