Perhaps the central dilemma in national security policy is how to A reconcile the obvious potency of nuclear weapons for purposes of deterrence with their dubious utility as instruments of defense—i.e., for fighting a war at tolerable cost in case deterrence should fail. In prenuclear days, deterrence was more or less a function of an efficient capacity for defense, but with the new technology deterrence may be accomplished with capabilities and threats that do not correspond to the capabilities and strategies most suitable for rational military action. This dichotomy forms the leading theme of Deterrent or Defense, by Captain B. H. Liddell Hart, one of Britain's leading military analysts. The book is a collection of articles written mostly during the past three or four years, and concerned chiefly with military problems of NATO. As in many books of this sort, the articles overlap to some extent and are not always consistent. Leaving aside the inconsistencies for the moment, Liddell Hart's basic position can be stated briefly. Strategic nuclear airpower is useful for deterring an all-out nuclear attack on the United States or a full-scale conventional assault on Western Europe. But it has no value whatever for purposes of defense, because the inevitable result of the actual use of such weapons is simply “mutual suicide.” Even though it would be “lunacy” for the United States to initiate thermonuclear war in response to a Soviet attack in Europe, the Russians' fear of such a response probably is still strong enough to deter them from all but limited actions. Hence, the major problem facing NATO is to develop an effective non-suicidal defense against limited aggression. The book's greatest merit lies in its contribution to the solution of this problem.