[mookiemookie]

I don't think the U-boat was necessarily a flawed design. I think bureaucracy was the fatal flaw in the U-boat arm. The U-boat was designed with the war it had to fight in mind. Smaller size wasn't a downfall as the Atlantic theatre was smaller than the Pacific. They didn't need to be as big as fleet boats. Especially once the U-boat bases on the coast of France were established.

If Doenitz had the numbers he asked for in the beginning of the war, they would have certainly been able to put more of a stranglehold on Britain. You can blame Hitler's obession with battleships and the misallocation of resources towards surface ships and the Graf Zeppelin project, when they could have been used to build up the U-boat fleet to the critical mass needed in order to completely encircle Britain.

There's certainly a lot of decisions that were made that bring up a lot of "if's". If Hitler hadn't been so obssessed with keeping boats out of the action defending the coasts of Norway against an invasion that never came, and sending them on suicide missions through the Med trying to help Rommel, they would have been able to focus on the Atlantic where they needed to be. If the development of the Type XXI was given the priority it deserved instead of being relegated to the back burner once the war was "won", they would have had that asset available. If the schnorkel had been installed in boats prior to 1943, it would have helped tremendously. If the Germans had realized the importance of radar (going back to your point about the Battle of Britain...one of the major blunders of the Luftwaffe was not taking out British radar installations which gave the RAF early warning enough to scramble during air raids), they would have certainly made more progress in that arena as well. It's not like the technology was unknown to them, it's just that they didn't know how to use it.