They were the machines that were so secret, even the staff working day and night to crack them didn't really know what they were.
But breaking the Lorenz SZ42's code was a breakthrough moment of the Second World War.
Now, more than 70 years on, the three crucial elements that led to that breakthrough have been reunited at Bletchley Park.
Firstly, there is the Lorenz machine itself - Hitler's cipher machine that took the technology developed in the Enigma and made it even more difficult to decode.
It is the first time it has ever been to Bletchley and has been loaned to the National Museum of Computing from Norway.Without a version of the machine, Newmarket scientist Bill Tutt had to find a way to crack the code without ever having seen one.
His breakthrough meant engineers could build Colossus. Allowing them to decipher messages within days rather than weeks.
"It's a very, very effective and complex machine and it took him three months with pencil, paper and probably a lot of caffeine to produce the logical diagram of the structure of the machine.
Next is the Nazi teleprinter which volunteers at Bletchley snapped up for £9.99 after spotting it for sale on EBay in Southend.
Although not in great condition, its significance was quickly realised.
"When we knew exactly what it was, when we got it back here to the museum and took the cover off, mice had been in it and nested, it had got wet at some stage - so it was in quite a bad state.
And finally - the veterans, who returned today to finally see the place they called home throughout the war tell the full story from Berlin to Bletchley for the first time.
Among the information they deciphered 70 years ago was key intelligence about events such as D-Day.
As she worked on the machine in June 1944, WREN Irene Dixon had no idea her husband-to-be was preparing to storm the beaches in Normandy.
It was not until decades later she was able to understand the part she and others had played.
"At the time, there was a war on, you just accepted it. I didn't know it was a new machine, I just got brought in and shown this great big machine and they said 'you're going to learn to work on it' and that was it. You just got on with your job."
Watch Claire McGlasson's report below.