I read up on Drumbeat a while back and the presence of U-Boats off the US coast was such an unexpected turn of events they were completely caught off guard. There are many eyewitness reports of people on the coast of America seeing ships getting hit by U-Boats, which means in the opening days and weeks, they operated very close to land with relative impunity.
I've yet to take part in Drumbeat as this is only my second IX career compared to 4 VII and 2 Type II, the first one ended west of Gibraltar in September 1940 after I got truly massacred by a convoy's escorts. I escaped, but due to Longer repair times mod and the sheer amount of damage I eventually abandoned the boat west of Portugal due to overwhelming flooding 2 days later. I should have headed to the milkcow NW of Gibraltar but I underestimated the extent of the damage and overestimated my crew's ability to fix it...
I'm currently celebrating New Year 1941 in port so yeh, America here I come soon!!