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A hundred people who worked at the famous centre whose codebreaking work helped shorten World War Two have had a reunion.
They were at Bletchley Park in Milton Keynes on Sunday 4 September 2011 for their Armed Forces Weekend, which was a chance for everyone to speak to the very operators who helped break the coded messages from World War Two.
85 year-old tour guide Ruth Bourne says events like these are important, 71 years on: "It emphasises we existed because we had to all sign the Official Secrets Act - which meant we couldn't tell anyone what we did."
Ruth was just 14 when she worked alongside the codebreakers at Bletchley Park. We asked Ruth why she thinks this public ReUnion is important to her and her colleagues. "It's really quite interesting the spirit of camaraderie is still there. Although sometimes we expect to see somebody, but sadly because of our ages, that person is no longer with us, and we're particularly sad when that happens. But somehow or other we are pleased we can still be there and have a day and reminisce.
BLETCHLEY PARK - FROM THE NATIONAL CODES CENTRE
Enigma became the backbone of German military and intelligence communications. But it wasn't invented as a secret and secure military communications system - it began in 1918 as a secure way of dealing with banking communications details - however it was the German military which saw the potential.
The Nazis thought it was unbreakable - the complex nature of the Enigma code - meant the odds against anyone who did not know the settings being able to break the code, where 150 million million million to one.
After breaking the basic code in 1932 when it was undergoing trials, the Poles managed to reconstruct a machine and passed on their knowledge to the British and the French. This enabled the codebreakers to make critical progress in working out the order in which the keys were attached to the electrical circuits, a task that had been impossible without an Enigma machine in front of them.
Armed with this knowledge, the codebreakers were then able to exploit a chink in Enigma's armour. A fundamental design flaw meant that no letter could ever be encrypted as itself; an A in the original message, for example, could never appear as an A in the code. This gave the codebreakers a toehold. In January 1940 came the first break into Enigma.
Encrypted signals were captured from a series of wireless intercept stations dotted around the UK - and sent them onto Bletchley Park to be decoded and analysed.
To speed up the codebreaking process, the brilliant mathematician Alan Turing developed an idea originally proposed by Polish cryptanalysts. The result was the Bombe: an electro-mechanical machine that greatly reduced the odds, and thereby the time required, to break the daily-changing Enigma keys - it was the Bombe that Ruth worked on!