I am aware that in 1945 we had a strictly limited number of Bombs. However, if they were our only effective method of destroying Germany it is possible additional resources would have been pitched in earlier and we could have had more by 1945. Or possibly what they produced was all that was possible.
Or we sit in UK for a year and then nuke the crap out of Hitler with our next batch of a couple dozen Bombs. It’s not like he’s got anywhere he can hide.
A more interesting scenario is whether UK would have fallen without an Eastern Front to divert the vast majority of Hitler’s forces.
In 1944 the Western Allies faced 1.5M to 2M Germans and allies. The Red Army was dealing with about 4M. How do you think things would have worked out for US/UK had they faced another 3M Germans in France and Italy?
The numerous factors involved make it difficult to compare numbers, but in general the western allies had to deal with about half the number of Germans that the Reds did.
In 44/45 we had about 5M men on the western front, facing about 1.5M Germans. And we still had a difficult time.
The answer to this question is not the same as the answer to the question about how things might have fared on the continent without a Russian front, with which you have conflated it.
The answer to this question is unequivocally: "No." Hitler had no practical ability to invade Britain, and was repeatedly told this by his admirals. Doenitz in particular told him that he had no chance of putting an invasion fleet in the channel against the British Navy alone, and certainly no chance against the combined US and British Fleets. Goering's ill-fated attempt to "invade" Britain from the air tells you all you need to know about whether Britain would have fallen to the Axis.
The number of bombs that the US had at the time that Oppenheimer left Los Alamos at the end of September 1945 is pretty well established as either 4 or 5. The KGB archives verified this number was known to the Russians as well.
I don’t believe any further resources could have been devoted to the production of atomic weapons without a detrimental effect on the conventional war. You must also remember that at the time there was no guarantee that an atomic weapon was even possible.
I agree with you that Hitler’s greatest mistake was his premature invasion of the USSR. Had he waited until he had consolidated his invasion of France and at least subdued Britain he had a chance of victory (small after the US entered the war).
I believe that Hitler’s hatred of and belief in the inferiority of the Slavic races overcame his understanding of the dangers of a two front war.