Between 2001 and 2003, nautical archaeologist Innes McCartney discovered and surveyed fourteen of the U-boat wrecks;[6][7] including the rare Type XXI U-boat U-2506, once under the command of Horst von Schroeter; the successful Type IXC U-boat, U-155 commanded by Adolf Piening and the U-778, which was the most promising salvage.[citation needed]