Destruction of that stuff after armistice or surrender is just a bloody waste of assets, does no good to no one. Not to mention the poor crews.
All German victories against the Royal Navy came at an incredible cost in men and material and were at best fleeting (no pun intended), regularly we got our asses kicked. But it's true what you say about Scapa Flow and Prien: The operation was masterminded by Dönitz, then admiral of the U-Boats, later on of the whole German navy, also Hitler's successor in the last days of the Reich, who was a U-Boat commander in WW I where the same thing was tried but failed. Plans for a (renewed) submarine sneak attack on Scapa Flow went as far back as pre-war thirties, the German Navy dreaming and scheming.
The strategic effect was nil though: The Royal Oak sunk by Prien was a swimming WW I museum that wouldn't have seen action against Germany's new line of battleships and cruisers anyway (all of them of 30ies origin, anything else we had was scuttled in Scapa Flow following the Versailles Treaty). Again poor crew though.
I was in Scapa Flow/Scotland two years ago - in every church there is a memorial plaque for the casualities, but the Scots - good sports that they are - never fail to mention "sunk by Captain Günther Prien and his crew in U-Boat ...", more than grudging respect.
