The Nazi U-boat submarine U-2513 was commissioned on October 12, 1944, as the war was winding down. Its captain surrendered to the allies on May 8, 1945 and it was taken to Oslo, then Ireland, then turned over to the United States where it actually become part of the U.S. Navy fleet.
On November 21, 1946, President Harry S. Truman took a tour of the U-2513 and became the first American President to travel on a submarine. It dove went 440 feet below the surface with the President on board.
The U-boat served the U.S. Navy well, with activity in Florida, New Hampshire, and Virginia.
But then in 1949, something odd happened. The submarine was taken out of service and sat idle in Portsmouth, even though it was still a perfectly fit vessel. In 1951, the Chief of Naval Operations ordered that the boat be sent to Florida - and sunk. And the order came down to specifically junk it in the remotest location of the Florida Keys - a spot northwest of the Dry Tortugas (Coordinates: 24°52.015′N 83°18.594′W).
Due to the sunken ship's extreme depth and remote location, few divers have ever attempted to visit it.