In late November , communist China began to turn over its cards. It had already covertly sent troops into North Korea. … With the Chinese intervention, the United States confronted a hard truth: Threatening a nuclear attack would not be enough to win the war. It was as if the Chinese hadn’t noticed—or, worse, weren’t impressed by—the atomic-capable B-29s waiting at Guam.
President Truman raised the ante. At a November press conference , he told reporters he would take whatever steps were necessary to win in Korea, including the use of nuclear weapons. Those weapons, he added, would be controlled by military commanders in the field.
In April of the next year, Truman put the finishing touches on Korea’s nuclear war. He allowed nine nuclear bombs with fissile cores to be transferred into Air Force custody and transported to Okinawa. Truman also authorized another deployment of atomic-capable B-29s to Okinawa. Strategic Air Command set up a command-and-control team in Tokyo.
This spate of atomic diplomacy coincided with the end of the role played by Douglas MacArthur. … Truman replaced him with General Matthew Ridgway, who was given “qualified authority” to use the bombs if he felt he had to.