And one must take into account the nearly unlimited budget, single minded purpose and the world's best scientists on the job. All of this means they are going to produce it. They really left no stone unturned in the quest to make the bomb. IMHO, with some luck, The Bomb could have been produced even earlier...
Hmmm so WI the US catches a lucky break and the bomb is ready for deployment by, say, shortly after D-Day?