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.

Posted on June 3, 2011 at 1:49 PM13 Comments


Jon June 3, 2011 6:41 PM

I’m just hoping they never have to take their museum on a tour. Could you imagine trying to explain deliberately putting a Bombe on an airplane?

just kidding 🙂

pointless_hack June 3, 2011 11:05 PM

“Those who do not learn from history…” – all cliches are true.

I long ago chose my moniker out of an affinity for just this kind of thing.

Lolz for me!

Philip Collier June 4, 2011 5:11 AM

Congratulations to the team for a job well done! This will be an important learning exhibit for people interested in the history of cryptography. Reading about a Tunny or Bombe is one thing; seeing one in real life (or building one) teaches how tough it really was to break those WWII cryptosystems.

Emile June 4, 2011 5:53 AM

If you have a chance, Bletchley Park is a great place to visit. The working Colossus is worth the visit by itself, the Bombe is impressive and I can’t wait to go back to see the Tunny.

John June 4, 2011 10:55 AM

While at BP do visit the independent National Museum of Computing on the same site. They do not get any money from the code breaking museum and are well worth supporting.

Catherine in Athens June 4, 2011 2:50 PM

How wonderful! I’ve been to Bletchley Park twice, but I’d like to go back to see the Tunny. Thank goodness there were a few memories they could use in the rebuild. Amazing to think that there were not full records in some archive somewhere.

Dirk Praet June 5, 2011 6:28 PM

Note to self: take train to Bletchley Park on next visit in London instead of spending all my time at the Forbidden Planet.

BF Skinner June 6, 2011 6:51 AM

“a working Tunny to complement their working Colossus and working Bombe”

Just need a working 3rd Reich to complete the set and Bob’s your uncle.

Jonadab June 7, 2011 9:06 AM

If I lived anywhere near close enough, I would definitely take a weekend and go see that.

(I’m afraid it’s a wee bit too far from central Ohio for that, though, particularly since I’m not really in the right economic bracket for discretionary plane trips.)

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Sidebar photo of Bruce Schneier by Joe MacInnis.