Recently declassified documents reveal that during Richard M. Nixon's first year as president, advisers on his White House staff were willing to revisit the question of whether to employ nuclear weapons in Vietnam. Senior officials and policy advisers in the administrations of Dwight D. Eisenhower, John F. Kennedy, and Lyndon B. Johnson had previously considered the possibility of using nuclear weapons to deal with military crises, influence negotiations, or terminate conflicts, but their deliberations had come to naught because of a deeply ingrained "nuclear taboo." ..
...Kissinger and his staff had begun by at least early July to develop contingency military plans under the codename "Duck Hook" (a term probably borrowed from golf parlance). To evaluate the secret plans prepared by members of the Joint Staff in Washington and military planners in Saigon, Kissinger set up a special NSC staff planning committee dubbed the "September Group" (aka "contingency group"). "I refuse to believe that a little fourth-rate power like North Vietnam does not have a breaking point," Kissinger confessed. "It shall be the assignment of this group to examine the option of a savage, decisive blow against North Vietnam. You start without any preconceptions at all." The president, he told them, wanted a "military plan designed for maximum impact on the enemy's military capability" in order to "force a rapid conclusion" to the war.
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