200-300 U-Boats.... Could Germany have crewed so many so early in the war???? Had Germany been able to apply a choke hold by sea, the only supply would have been by air. The US had a very hard time with the Berlin Airlift when it had started, and the Air Force was full of cargo planes after the war. It was not until large four engine cargo planes were put into service that sufficent supplys could be brought in to support Berlin. That was to supply only one city, I hate to imagine how much would have to be flown in to support the entire british islands! In 1940 the US trying to supply the Brits by air would not have been pretty. Also, early in the war, the US east coast was easy pickings for U-Boats. With 200+ boats, Germany could have sunk everything that left the east coast. Until the small yellow airplanes showed up.