U-Boats Were the Key
We haven't had a good military history topic for a while, so how about this one . . .
I believe it may be logically argued that Germany could have won at least a limited victory in World War II had she concentrated more heavily on the design and production of her U-boat arm. Germany began the war with only about 50 U-boats, some of which were useful only for coastal patrols. Had she started the war with twice that number of Type VII and Type IX U-boats, she could have succeeded in effectively closing the Atlantic to American resupply of Britian. This would, I think, have resulted in a surrender of Great Britain by early 1941. Without a base from which to operate in Europe, the United States would have been unable to launch any sustained attack on mainland Europe, and Hitler would have succeeded in his bid to control all of Western Europe and its resources. Without the necessity of maintaining large forces in the West, Operation Barbarossa against the Russians in the East would likely have succeeded.