Despite there being no original parts left of the Tunny machine post-WWII, a crack-team of British computer boffins were able to rebuild the code-cracking machine, which played a huge part in intercepting Hitler's commands.
It took six years, but finally the National Museum of Computing has a working Tunny machine, identical to the one used by the Allies, which were recycled for spare parts after the war. Somehow, the original circuit diagrams were lost when the 12 - 15 machines were dismantled, with it rather comically believed that the diagrams were used as toilet paper. Luckily the circuit notes survived, and the team was able to build a machine from scratch, going by them and some of the engineers' memories.
The video over on the BBC's website shows an interview with one of the operators of the original Tunny machines, Helen Currie, who says that they weren't allowed to tell anyone what their jobs were, until about 30 years after the war ended—such was the secrecy of their positions. In fact, some of the Nazi messages they intercepted actually led to D-Day, as it helped the Russians during the battle of Kursk. [BBC]
Image Credit: Bletchley Park via ZDNet