In the case of Korea, the use of tactical nuclear warheads against the People's Republic of China in late 1950 was a very real strategy, and a one even championed by the Joint Chiefs in the event Chinese troops crossed the Yalu river. However the use of nuclear devices was turned away by the Truman administration for several reasons;
- The US recognized the severe consequences diplomatically if it resorted to tactical nuclear weapons. Britain's Prime Minister Clement Attlee was vehemently opposed, and echoed many of Truman's advisers in acknowledging the potential diplomatic fallout (no pun intended) in Moscow.
- Washington remained skeptical of SACs ability to launch successful nuclear strikes, especially against the USSR should it choose to intervene. Jet-powered delivery systems and nuclear-capable aircraft carriers only came into force around 1953.
- The State Department intentionally dragged its feet about the deployment of nuclear weapons outside of US soil, meaning that the High Command inside the Pentagon had no immediate nuclear strike capability in Korea.
- The US remained aware of the USSR's increasing nuclear capabilities. Though the Soviet's had detonated their first nuclear weapon only the year previously, their abilities to launch strikes against the contiguous US and Western Europe was growing.
- North Korean and Chinese infrastructure and troop concentrations were widely dispersed across the countryside. By October, Pyongyang was largely in ruins from its capture and months of US bombing. It was not believed a nuclear strike could provide a decisive blow against a scattered KPA or the enormous PLA.
In Vietnam, many of the reasons for deployment of nuclear weapons remained much the same;
- The USSR and China were large suppliers of arms and munitions to the North Vietnamese Army and the Viet Cong. Though not officially, large numbers of Soviet and Chinese pilots and military advisers were present in North Vietnam. A nuclear strike may well have been a trigger for war.
- If not a direct cause of war, the breaking of the 20 year 'taboo' on nuclear weapons would have been a crippling propaganda defeat for the US.
- Many of the US' allies were opposed to the use of nuclear weapons and the conflict in Vietnam, especially Britain and Japan. The US would likely lose many of its critical forward operations bases.
- Soviet nuclear capabilities had expanded rapidly, and the threat of retaliatory ICBM strikes against the US homeland was a real possibility.
- The NVA and VC executed a primarily guerilla campaign, in Vietnam as well as Laos and Cambodia. A nuclear strike against such widely dispersed forces would have had very little effect.
- Most also operated independently from Hanoi, so a strike against the North Vietnamese capital wouldn't have greatly effected their ability to wage war in the South.
- The Vietnam war was already proving incredibly unpopular at home, with growing numbers of people protesting the draft and campaigning for nuclear disarmament. Combined with a growing civil rights movement, a nuclear strike and the immediate possibility of retaliation may have ignited significant civil unrest.
Sources used:
Dingman, R. 'Atomic Diplomacy during the Korean War', in International Security. (1988). 50-91.
https://www.cia.gov/library/readingroom/docs/DOC_0001166479.pdf