Hundreds of U.S. Ships? Could you provide proof? I am only aware of two U.S. ships sunk: the SS Housatonic, and the SS California, both in February, 1917. (Germany had ended unrestricted submarine warfare from September 1915- February 1917)
Those are the two AMERICAN ships (and one was all that was necessary to declare war, my friend). But there were hundreds of neutral ships or ships carrying passengers/neutrals that were no Americans. The fact that the Germans only resumed this as a desperation ploy suggests that they knew it was wrong. They didn’t dare take on the British navy, even with all their U-boats.