[kiwi_2005]

IMO If the XXI was around in 1940 Germany would of defeated Britain in the atlantic war. But they then would of had a new problem - america. And no doubt subs do get captured, fate would have it that a XXI would of fallen into the allies hands where say america with their huge production line would of made there own versions of the XXI and put more out than what germany could.

Also America/Britain slowed down the production of uboats with bombing raids on bases this would of been another problem.