The Nazi's Enigma Machine - and the mathematics behind it - was a crucial part of World War II. Flaw video at: http://www.youtube.com/watch?v=V4V2bpZlqx8
More links & stuff in full description below ↓↓↓
Brown papers on ebay: bit.ly/brownpapers
Dr James Grime demonstrates the machine and discusses its many configurations.
James' "day job" is touring with the Enigma machine - he could even visit you - see more at http://enigma.maths.org/content/project-officer