U-1105 BLACK Panther (Type VIIC German Submarine) National Register of Historic Places Listing

It wore a skin of black rubber. The Kriegsmarine called this experimental acoustic-camouflage coating Alberich, a four-millimeter-thick synthetic rubber designed to swallow Allied sonar pulses and keep the submarine invisible in the deep. It worked pretty well, actually. In April 1945, the submarine torpedoed and crippled the British frigate HMS Redmill off Ireland, slipping away into the dark before the escort group could pin down its location. Only about a dozen U-boats ever got this rubber cladding, which makes the wreck of U-1105 an incredibly rare survivor of late-war Nazi stealth technology. The Allies wanted those secrets.

So, after Germany surrendered, the Royal Navy handed the boat over to the United States. The US Navy brought it to the Potomac River to dissect the adhesive that kept that rubber stuck to the steel hull under immense pressure. They learned a lot. Then they blew it up. In 1949, navy researchers detonated a 250-pound depth charge just thirty feet from the submerged hull, cracking its spine and sending it ninety feet down to the muddy bottom near Piney Point. Not an easy dive, though. Strong currents and near-zero visibility protect the wreck far better than modern state laws do, keeping the peeling rubber tiles and intact conning tower preserved in the cold, brackish water.