The Atlantic front was a major battleground for the American and German/British fleets. At day, you had US battleships blockading British ships bound for Canada and German Zeppelins being shot down by American P-51 fighters(which was why the Germans could send little reinforcements). At night, German submarines sunk ships carrying arms to Ireland to help the insurgency. The height of these battles occurred with the Minnesota class battleship (Much more powerful than the Iowa ATL and they could also carry a small amount of aircraft to boot) coming out of the Florida and Texas shipyards. These would prove vital in the war effort. The battle seesawed between the Americans and the British, culminating in a showdown between the USS Minnesota and the Tirpitz/Hood in August 20 1942, with the Minnesota surprisingly victorious, leaving both the Hood and the Tirpitz dead in the water. the Minnesota however was so badly damaged that the repairs were not complete until after the war was over.
however the Germans countered with the H-Class Superbatleship, which was more powerful than any ship afloat apart from the Japanese Yamato class. however the H-Class arived to late in the war to have any affect.
Note: there was no U-Boat campaign, since America could use its own oil and had its own food supply.