NATO did not exist in 1948. It only came into force in 1949
US had some 50 bombs in 1948 (see reference above)
There were only 35 silver-plate B-29 in 1948. Just one sortie will limit any follow-up in a bad way.
Wiki (for good or bad) says:
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Believing that Britain, France, and the United States had little option than to acquiesce, the Soviet Military Administration in Germany celebrated the beginning of the blockade. General Clay felt that the Soviets were bluffing about Berlin since they would not want to be viewed as starting a WWIII. He believed that Stalin did not want a war and that Soviet actions were aimed at exerting military and political pressure on the West to obtain concessions, relying on the West's prudence and unwillingness to provoke a war. Commander of USAFE General LeMay reportedly favoured an aggressive response to the blockade, in which his B-29s with fighter escort would approach Soviet air bases while ground troops attempted to reach Berlin; Washington vetoed the plan.
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Amazingly, The Berlin airlift could then also have resulted in a US attack and then who is to blame when it goes 'pear-shaped'?
After all, Winston had his dream of
Operation Unthinkable' which was a
US/UK surprise attack on Russia. We have looked at that one and it is of course very feasible that say Poland would welcome 200,000 SS troops coming along - again - to liberate them (sarcasm rules OK).
As I mentioned above, nuclear drops would have to have been by B-29. It is not likely that all would have gone through, so where would the bombs have landed? France and Germany is my suggestion.
If Washington had supported LeMay we would have had
Operation unthinkable in 1948 (versus June 1945 as was Winston's idea).
How well-prepared was US (in Europe!) for WWIII? I believe the draw-down was rather extensive which means that the USSR had the upper-hand in tanks and infantry and aircraft.
Rescuing a country from communism by killing all its people, devastate the industry, poison the soil and making it inhabitable for hundreds of years is not a great option. And that could well be the result for Germany and Poland.
Even with a total of (only) 1,25 Mega-tons of nuclear bomb power in 1948, devastation is indeed assured.