World War II Tunny Cryptanalysis Machine Rebuilt at Bletchley Park
The rebuild team had only a few photographs, partial circuit diagrams and the fading memories of a few original Tunny operators to go on. Nonetheless a team led by John Pether and John Whetter was able to complete this restoration work.
Pether explained that getting the electronics to work proved to be the most difficult part of the restoration process.
“We’ve succeeded in rebuilding Tunny with scraps of evidence, and although we are very proud of our work it is rather different from the truly astonishing achievement of Bill Tutte’s re-engineering of the Lorenz machine,” he said. “Sourcing 200 suitable relays and dealing with the complex wiring schedules was difficult, but we really got in tune with the original team when we had to set up the electronic timing circuits. They were a continuous source of problems then as they are even now for the rebuild team—except the original team didn’t even have the benefit of digital storage oscilloscopes.”
The rebuild took place in four stages: the construction of a one-wheel Tunny to ensure that timing circuits and relays worked correctly, followed by progressively more complex five-, seven- and 12-wheel Tunny. At each stage, the rebuilds were tested. Key components for the Tunny rebuild were salvaged from decommissioned analogue telephone exchanges, donated by BT. The same components were used to complete the earlier Colussus rebuild project.
Now they have a working Tunny to complement their working Colossus and working Bombe.