Some historians believe that the closest the United States came to using atomic weapons in the Korean War was in April 1951. At that time, atomic bombs were actually being made ready in Okinawa for deployment against targets in China and the Soviet Union (MacArthur planned to target Vladivostok, according to a recent documentary I saw on the subject). However, pressure from Britain, France, and other NATO allies persuaded Truman not to proceed.
But what if the decision to deploy the weapons had been made, and on April 30, 1951, the United States drops 20 atomic weapons on targets all over Manchuria and as far away as Beijing and Vladivostok?
At this time, the Soviet Union has a very small arsenal of atomic weapons and virtually no capacity to deliver them to the United States. However, it has a very large army and military estimates at the time were that Stalin's response would be to immediately invade Western Europe. The relatively few Soviet atomic bombs can be assumed to be used in this campaign as well.
The United States had about 300 atomic bombs at the time. NATO conventional forces in Europe were not capable of stopping a Soviet invasion, so atomic weapons were to be deployed there to stop such an attack.
The question is, will Stalin launch the invasion, knowing that to do so would likely mean atomic annhilation of the Soviet Union?
What else could Stalin do if he doesn't launch the invasion in Europe?
If he does launch the invasion, will the NATO allies allow the United States to deploy atomic weapons on their soil to stop the Soviet thrust?