There was no recorded wreck at this site so it had been described to your relevant authorities, such as the Receiver of your Wreck (RoW). They were regarded as outstanding boats. In the course of the war eight had been sunk, three surrendered and had been at some point scrapped, https://u3102329.theblogfairy.com/33302475/the-smart-trick-of-u31-that-nobody-is-discussing