The U-151 was the first German U-boat to operate in U.S. territory in World War I. The U-151 is not actually sunk in these waters ( it was sunk deep off Virginia after the war, ) but it did "contribute" the following six shipwrecks, all on the same day, Sunday, June 2, 1918:
The United States Coast Guard has donated a number of vessels as artificial reefs over the years. They seem to be sensitive about having their vessels shown in a "bad" way, and typically paint out all the markings before turning them over.