forces. Conventional forces were to serve two functions, a deterrent function and the function to fight limited wars. The main argument of the Eisenhower administration had been that conventional forces were too costly and nuclear weapons would have "more bang for the buck."
Kennedy wanted to deter all wars, general or limited, nuclear or conventional, large or small. Eisenhower and Dulles wanted to achieve similar goals but at minimal cost. Their risk was to either not act at all or respond at all levels of threat beyond the original provocation. Kennedy disregarded costs and emphasized sufficient flexibility to avoid either escalation or humiliation. In particular Kennedy wanted to increase the range of available options prior to resort to nuclear war. The threshold beyond which the President might have to decide to initiate the use of nuclear weapons had to be raised. Also, the damage caused by a war with tactical nuclear weapons seemed to high. Furthermore, Kennedy believed that the European allies should contribute more to their defense. Moreover, a continued reliance on nuclear weapons could lead to their further proliferation. The basic idea of Flexible Response, however, was to increase the ability to confine the response to non-nuclear weapons.
McNamara had originally thought new conventional weapons weren't needed. The Berlin Crisis (1961-1962) convinced him that additional troops were needed not only as a sign of resolve to the Russians but more specifically to increase the number of escalatory steps.
Differentiations of Flexible Response
Ladder of Escalation
Countervalue and Counterforce Strategy