The raid on Scapa Flow. Looking for info.

[Von Due]

I am looking through accounts, reports, moves, docus etc on Prien's raid on Scapa Flow and one thing sticks out as missing:

The planning phase.

Now, it is my understanding that there was an extreme level of secrecy surrounding the planning, with most of the admiralty unaware of the plans, only a handful of intelligence officers and operatives, together with Dönitz and a very few selected lot in the know. No submariners, including Prien, had any idea.

As such, there is no surprise that little is known about the planning phase. I don't know what happened to the documents after the raid, if they were destroyed or kept secret, or if they were found after the war, or if Dönitz himself told the story after the war.

The "memoirs" of Prien are of little interest as they aren't the actual story, not even penned by Prien but ghost writers paid by the Party. There is one German feature film from the 50's but the little I have seen from it, it is not exactly a docu drama to say the least. Other docus focus pretty much solely on the raid itself, and the fate of the boys and men onboard Royal Oak. Again, nothing on the actual planning.

So, I'll ask here seeing we have a crowd of people with perhaps an above average interest in naval history: Have you any links or tips to docus or accounts on the planning, from intelligence gathering to the details of the plan?

EDIT: Forgot to mention, I have found this http://www.u47.org/english/u47_sca.asp which includes some insight at least.