Thursday, January 14, 2010

My first day on the bombe…

Last week was my introduction to the Bombe in Bletchley Park. I had volunteered last year to be a demonstrator and I was going there to find out more, and also for John H who ran the rebuild project to check me out and gain confidence that I might be up to it – a mutual interview as it were.

My first challenge was to get there, having woken early I looked out on a whiteout, snow had reached East Anglia again, and there were a good few inches of snow on the ground, and it was settling well. I live in a very rural area, and there would be no gritted roads for some distance. Driving a powerful rear wheel drive car would also add some extra fun into the equation :-). At least I had fully de-iced the car the day before so that I could get away fairly quickly!

In the end I convinced myself that the weather would not deteriorate and set off early into the falling snow. The next hour saw me travel all of 2 miles as all traffic seemed to have come to a halt in our area, so I went ‘off-piste’ as it were and got to the gritted main roads and then got to BP only about ½ hour later than expected.

I met up with John H, Mike and Paul - 3 stalwarts of the Bombe project. First up was coffee (very welcome!), and then we covered H&S issues – the conversation went along the lines of
“been electrocuted?”
“yup (shows scar on thumb), full mains for 5-10 seconds right hand to left and left with back injury (spondylolisthesis if you are interested) to prove it. Oh and I’m sufficiently risk averse to have this in my pocket (holds up snow/ice scraper for car)”
“so you’ll be sensible around 200V DC then… …now this is the instruction sheet for starting the Bombe, let’s start”
OK, so I abbreviated, paraphrased, and been a bit facetious.
But H&S is taken seriously on the project in the practical environment so we don’t need a nanny state approach to things!!

So then it was time to run the Bombe. The Bombe rebuild project was more an engineering project than anything else so as a computer graduate and geek, rather than an engineer I come to the project with a different focus.

The conversation we had around just 1 A4 sheet of detailed instructions is lengthy as the geek in me comes out and pursues different angles and more than 1 cul-de-sac; but we get through it all and I finally push the last button and it’s running!!! The 13 year old in me was completely satisfied and delighted, and grinning away, although I try to convey a quiet satisfaction externally. We stop the machine, and I discover my placement of the wheels was not precise enough and we have had “slippage”. We fixed that by throwing the special switch which speeds the Bombe back to ZZZ and then stops. I reposition the wheels and things then work fine.

At about this point some visitors came through and were asked (not my me!) if they wanted to see it running - carefully following my instructions again I did my first live (as it were) demonstration. It worked as it should, and this time did not slip – hurrah!

We switched off and then I throw the instructions into reverse and shutdown and dis-assemble my part of the Bombe.

Well that went well!!

So we went off to see Kelsey Griffin and thence to lunch in Hut 4.

On returning to the Bombe, we spent some time looking at the demonstration ‘cut down’ Bombe which is being built so that visitors can see a much smaller machine running on demand (and without the need for a demonstrator) in the same way as the real thing. This will be a great addition to the exhibition as the noise and movement makes the Bombe so tangible rather than a boring static box of tricks. There are a number of engineering issues, and I could not add much to what was going on, but I did enjoy the discussion about whether to move a component (or not) that ended with the question “Do you like hospital food?”. The component stayed where it was :-)

To get back on track with education I then went into the booth to view the splendid 3D presentation on the Enigma machine and the decryption work at BP. If you go, don’t miss it.

The final part to the day’s training was to spend some more time with John going through ‘menus’. During the war the cryptographers came up with cribs which offered clues to settings of the Enigmas in use with a particular code, and this resulted in a diagram of letters with connections between them. These are commonly shown in books, but I have always found some difficulty in understanding what went on (getting to them from the crib seems easier somehow).

John then very patiently went through a sample menu, and I then realised that the books and documentation I had read to date simply did not explain how much intellectual effort the Wrens who ran the Bombes went through to turn the menu into a practical wiring assembly. There’s a really complex set of decisions and wiring layouts to plan so that the menu can be turned into a Bombe run and thus reveal potential settings for the Enigma used for the original transmission. With each Bombe run taking a maximum of 12-13 minutes, there was not much time to plan the next run if it was not already prepared.

I’d like to think that sometime in the future I’ll fully understand all this, and be able to put it all together into something more publishable for the team.

Additionally the computer/maths graduate in me think there’s probably an algorithm in the process to be developed so that turning a menu into practical wiring would be semi or even fully automatic! Maybe 2012 :-)

With that we were done, and after a brief chat with Kelsey again, I hit the road and finally made it home. As I said on twitter on the day, that’s the highest bandwidth learning I’ve done since University days!


Bombe rebuild project - more information Bletchley Park is well worth a visit if you are anywhere near Milton Keynes, and for the techies amongst you it also houses
The National Museum Of Computing where both the Colossus rebuild (the world’s first computer), and Witch (the world’s oldest complete computer).

If you want to get involved with the Bombe project then contact Kelsey on twitter, or via the webpages mentioned above

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