CNET's 360-degree tour of Bletchley Park, now live on YouTube, takes you inside Britain's wartime codebreaking headquarters. Be sure to check it out, then click through our photos from behind the scenes at Bletchley Park, where we got up close and personal with an original Enigma machine.
Dominating the view of Bletchley Park is the mansion. Bletchley, in Buckinghamshire, was ideally situated as a codebreaking site since it was accessible from London as well as university towns Oxford and Cambridge, from which many codebreakers were recruited.
Much of the Bletchley codebreakers' time was consumed by this -- a German military Enigma machine. Enemy forces used these machines to encode their communications, and the encryption was devilishly hard to crack.
Enigma had one fatal design flaw, however. A letter could never be encoded as itself. So if you had an "a", you knew that letter wasn't really "a". Bletchley codebreakers also relied on "cribs", which were essentially best guesses at what a message could be about, and "pinches", where Enigma codebooks were stolen from the German military in the field.
Here's an individual Enigma rotor. The Enigma machine was used commercially as early as the 1920s -- but the evolving military variants added increasing levels of complexity, to make codes tougher to crack.
Making things harder is the plug board, which swapped letters with other letters of the user's choice. In total, an Enigma machine offered over 150 million million million possible settings combinations.
To read an Enigma message, all you needed to do was replicate the rotor positions and plug board settings on your own machine, and the code would be swapped back into readable text. But without knowledge of those settings, turning Enigma code into readable text was next to impossible.
Helping to crunch the numbers of possible Enigma settings combinations was the Bombe machine, a cumbersome, room-filling device pioneered by Alan Turing. Each wheel corresponded to an Enigma rotor position, and this electromechanical monster would rattle through possible settings combinations, hunting for configurations that made sense.