Through four decades the North Atlantic Treaty Organization (NATO) has based its deterrent on the principle that the United States would retaliate with nuclear weapons if a Soviet conventional attack against Western Europe succeeded. 1 This notion has long troubled most strategic analysts. It remained generally acceptable to political elites, however, when U.S. nuclear superiority appeared massive enough to make the doctrine credible (as in the 1950s); when the conventional military balance in Europe improved markedly (as in the 1960s); or when détente appeared to be making the credibility of deterrence a less pressing concern (as in the 1970s). None of these conditions exists in the 1980s, and anxiety over the danger of nuclear war has prompted renewed attention to the possibility of replacing NATO's flexible response doctrine (a mixture of nuclear and conventional deterrence) with a reliable conventional deterrence posture that might justify a nuclear no-first-use (NFU) doctrine. 2