|An Enigma Machine at Bletchley Park|
In order to decode the messages, you needed to know how the coded machine had been set up - which rotors had been used in which order and their start points. During the war, the settings changed every 24 hours, again to make the codes even harder to crack.
Although it all sounds quite complicated you can make a paper version of the Enigma machine very easily as someone has already done most of the work for you. You can download a paper enigma machine (this link will download a PDF) that fits perfectly round a pringles tube.
|Here's one @TeaKayB made earlier.|
You can then encode messages to send to others and as long as they know the settings you used to write your message they can use the same ones to decode it. Simple! I think this would be a great addition to anyone studying WWII as a topic or as part of a maths challenge all about codes and ciphers. I wonder if the children could even develop their own code machine along similar lines.
(If you want to see the real thing and learn about them in more detail then get yourself along to Bletchley Park in Milton Keynes. You pay £12 for an annual pass and can then visit as many times as you like - not a bad deal at all as there's way more than a day's entertainment there).