well here is the thing.
though the entry of the US into the war was a likleyhood i dont thing the Germans anticipated Pearl Harbor occuring... the German war declaration was a result of that attack so sending a U-boat on a long voyage to NYC would no doubt require advanced knowlege that the pearl harbor raid would take place and that Germany would declare war on the U.S. at a specific date.
I have used this tactic on a British port before. I had infinite fuel on at the time shortly after Grey wolves came out. Departed port and rished to Bristol or somewhere (i dont recall where) rushed in on the surface and nobody even batted an eye lash. i reveresed into a berth and submerged just hours before the war started. when the British map cities went to red i commenced my attack and sank a medium cargo, a large tanker, a cruiser and a couple of destroyers. because i was surrounded on the port, starboard and stern by concrete there was really no way they could attack me. when the action settled i rushed out to deep water.
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