The threat of a nuclear strike in Korea was real. As Chinese forces pushed back the United States forces from the Yalu River, Truman stated during a 30 November 1950 press conference that using nuclear weapons was “always [under] active consideration”, with control under the local military commander. The Indian ambassador, K. Madhava Panikkar, reports “that Truman announced he was thinking of using the atom bomb in Korea. But the Chinese seemed unmoved by this threat.
The PRC’s propaganda against the U.S. was stepped up. The “Aid Korea to resist America” campaign was made the slogan for increased production, greater national integration, and more rigid control over anti-national activities. One could not help feeling that Truman’s threat came in useful to the leaders of the Revolution, to enable them to keep up the tempo of their activities.”
On 5 November 1950, the Joint Chiefs of Staff (JCS) issued orders for the retaliatory atomic bombing of Manchurian PRC military bases, if either their armies crossed into Korea or if PRC or KPA bombers attacked Korea from there. The President ordered the transfer of nine Mark 4 nuclear bombs “to the Air Force’s Ninth Bomb Group, the designated carrier of the weapons … [and] signed an order to use them against Chinese and Korean targets”, which he never transmitted.
Many U.S. officials viewed the deployment of nuclear-capable (but not nuclear-armed) B-29 bombers to Britain as helping to resolve the Berlin Blockade of 1948–1949. Truman and Eisenhower both had military experience and viewed nuclear weapons as potentially usable components of their military. During Truman’s first meeting to discuss the war on 25 June 1950, he ordered plans be prepared for attacking Soviet forces if they entered the war. By July, Truman approved another B-29 deployment to Britain, this time with bombs (but without their cores), to remind the Soviets of U.S. offensive ability. Deployment of a similar fleet to Guam was leaked to The New York Times. As United Nations forces retreated to Pusan, and the CIA reported that mainland China was building up forces for a possible invasion of Taiwan, the Pentagon believed that Congress and the public would demand using nuclear weapons if the situation in Korea required them.
After his statement caused concern in Europe, Truman met on 4 December 1950 with UK prime minister and Commonwealth spokesman Clement Attlee, French Premier René Pleven, and Foreign Minister Robert Schuman to discuss their worries about atomic warfare and its likely continental expansion. The United States’ forgoing atomic warfare was not because of “a disinclination by the Soviet Union and People’s Republic of China to escalate” the Korean War, but because UN allies—notably from the UK, the Commonwealth, and France—were concerned about a geopolitical imbalance rendering NATO defenseless while the United States fought China, who then might persuade the Soviet Union to conquer Western Europe. The Joint Chiefs of Staff advised Truman to tell Attlee that the United States would use nuclear weapons only if necessary to protect an evacuation of UN troops, or to prevent a “major military disaster”.
On 6 December 1950, after the Chinese intervention repelled the UN Command armies from northern North Korea, General J. Lawton Collins (Army Chief of Staff), General MacArthur, Admiral C. Turner Joy, General George E. Stratemeyer, and staff officers Major General Doyle Hickey, Major General Charles A. Willoughby, and Major General Edwin K. Wright met in Tokyo to plan strategy countering the Chinese intervention; they considered three potential atomic warfare scenarios encompassing the next weeks and months of warfare.
In the first scenario: If the PVA continued attacking in full and the UN Command was forbidden to blockade and bomb China, and without ROC reinforcements, and without an increase in U.S. forces until April 1951 (four National Guard divisions were due to arrive), then atomic bombs might be used in North Korea.
In the second scenario: If the PVA continued full attacks and the UN Command blockaded China and had effective aerial reconnaissance and bombing of the Chinese interior, and the ROC soldiers were maximally exploited, and tactical atomic bombing was to hand, then the UN forces could hold positions deep in North Korea.
In the third scenario: if China agreed to not cross the 38th parallel border, General MacArthur recommended UN acceptance of an armistice disallowing PVA and KPA troops south of the parallel, and requiring PVA and KPA guerrillas to withdraw northwards. The U.S. Eighth Army would remain to protect the Seoul–Incheon area, while X Corps would retreat to Pusan. A UN commission should supervise implementation of the armistice.
Both the Pentagon and the State Department were cautious about using nuclear weapons because of the risk of general war with China and the diplomatic ramifications. Truman and his senior advisors agreed, and never seriously considered using them in early December 1950 despite the poor military situation in Korea.
In 1951, the U.S. escalated closest to atomic warfare in Korea. Because China deployed new armies to the Sino-Korean frontier, pit crews at the Kadena Air Base, Okinawa, assembled atomic bombs for Korean warfare, “lacking only the essential pit nuclear cores”. In October 1951, the United States effected Operation Hudson Harbor to establish a nuclear weapons capability. USAF B-29 bombers practised individual bombing runs from Okinawa to North Korea (using dummy nuclear or conventional bombs), coordinated from Yokota Air Base in east-central Japan. Hudson Harbor tested “actual functioning of all activities which would be involved in an atomic strike, including weapons assembly and testing, leading, ground control of bomb aiming”. The bombing run data indicated that atomic bombs would be tactically ineffective against massed infantry, because the “timely identification of large masses of enemy troops was extremely rare.”
Ridgway was authorized to use nuclear weapons if a major air attack originated from outside Korea. An envoy was sent to Hong Kong to deliver a warning to China. The message likely caused Chinese leaders to be more cautious about potential U.S. use of nuclear weapons, but whether they learned about the B-29 deployment is unclear and the failure of the two major Chinese offensives that month likely was what caused them to shift to a defensive strategy in Korea. The B-29s returned to the United States in June.
Despite the greater destructive power deploying atomic weapons would bring to the war, their effects on determining the war’s outcome would have likely been minimal. Tactically, given the dispersed nature of Chinese and North Korean forces, the relatively primitive infrastructure for staging and logistics centers, and the small number of bombs available (most would have been conserved for use against the Soviets), atomic attacks would have limited effects against the ability of China to mobilize and move forces. Strategically, attacking Chinese cities to destroy civilian industry and infrastructure would cause the immediate dispersion of the leadership away from such areas and give propaganda value for the communists to galvanize the support of Chinese civilians. Since the Soviets were not expected to intervene with their few primitive atomic weapons on China or North Korea’s behalf if the U.S. used theirs first, factors such as little operational value and the lowering of the “threshold” for using atomic weapons against non-nuclear states in future conflicts played more of a role in not employing them than the threat of a possible nuclear exchange.
When Eisenhower succeeded Truman in early 1953 he was similarly cautious about using nuclear weapons in Korea, including for diplomatic purposes to encourage progress in ongoing truce discussions. The administration prepared contingency plans to use them against China, but like Truman, the new president feared doing so would result in Soviet attacks on Japan. The war ended as it began, without U.S. nuclear weapons deployed near battle.