My grail is not so much what is not known but what was there before I knew.
I came across this clip a couple of years ago and sadly this is only up the road from where I live.....and I never knew. Now it is most likely never to run again and sits as a static display in RAF Cosford.
Imagine this in HD and digital audio.
https://youtu.be/jAcgUPjb16Q
Oh and how about;
The audio recordings made during the filming of "The Battle of Britain" movie in the 1960's. Imagine all the wonderful professionally recorded sounds captured during the making?
They could make a fortune selling the records as audio cd's
If only, cheers, MP