The correct answer is that it was about deterring the soviets from all out war by threatening a full nuclear response to any aggressive act.
Basically, what this means is that they announced that if there was even a slight possibility that the Soviets would attack them or if they did attack them, they would go full on with nukes on them and would not think about repercussions. This was later reverted as anyone with a clear head understood that nukes were not a good option.
