Once i late 1941 i was not far of Iceland in the night and bad weather and i came across a convoy I managed to sink a large merchant and sneak out the back of the convoy then surfaced and spoted a destroyer so i dived to periscope depth and realized that i was in the middle of a US task force with two cruisers of the Brooklyn class and a battleship of the Colorado class (I think but i can't remeber for certain) also numberous destroyers. I had a clear shot at the battleship and tempting as it was i dived and let it go.
(They weren't best pleased about the Ruben James let alone a battleship) .
Also on the east coast of the USA I've often come across a task force with destroyers and a Essex class aircraft carrier after the US join the war.