Dave: I agree that German lost when the US came in. A purely European war might have ended with all sides exhausted. I doubt Germany could have brought Russia to military collapse. Or Russia could have finished Germany. At some point the Empire would have not sacrificed more to support the UK.

But at a less abstract level the U-boats could only hamper supplies. As someone said we supplied Russia mostly from Alaska. If the North Atlantic had been cut by U-boats and England had fallen we would have shifted South to stretch their logistics. The South Atlantic across to Africa would have been a larger theatre of war.

At some point German logistics were certain to fail. They had at best, what, four million soldiers? And occupying large territories ties down large garrisons.

I don’t think anyone mentioned how much air patrolling hurt the U-boats. At the beginning of the war there were few long range patrol planes. None had radar.

The deficiency received high priority. The B-24 was the ideal platform. It could fly low and slow for thousands of miles. Radar kept the U-boats from running on the surface at night to recharge batteries and move to new positions.

Advocates of heavy bombers resented, for a time, the priority given to patrol planes. Good judgment prevailed. The allies paid more attention to operations research than the Axis.