The security risk if Germany discovered U-505's capture

How damaging would it have been if U-505's capture became public when it happened?

Germany would probably have changed its Enigma settings and code books quickly, jeopardizing the intelligence gained from the submarine.

The value of capturing U-505 extended beyond the submarine itself to its code material and equipment. If Germany learned promptly that the boat and its documents had fallen into Allied hands, it could change Enigma procedures and replace the code books in use. That response would reduce or remove the intelligence advantage gained from the capture. The operational challenge was therefore to conceal the event as well as seize the vessel. The exchange shows how boarding success, prisoner control, and information security combined in anti-submarine warfare.