I've posted three Numberphile videos about the famed Enigma Machine, featuring Dr James Grime.
The first explained how the machine actually works.
It ended with a cliff-hanger, and I intended to upload a short sequel (filmed at the same time) which explained the Enigma's fatal flaw.
However the first video created much interest and there seemed to be great expectations for the sequel.
So I made the three-hour round trip back to Cambridge to film a more elaborate conclusion.
I also uploaded this video of "extra footage" which didn't make the cut.
Some people might not realise that James' "day job" in traveling around the Enigma Machine and giving talks about it... More at this link.
The machine itself is on loan from author Simon Singh.
And to read an excellent article about the maths behind Enigma (written by James) - click here.