Friday, April 16, 2010

Bletchley Park #1

One reaches Bletchley from London, England, in the manner we described in a previous blog post. Once you're at Euston Station with your tickets, there are several choices of train. The best ones stop only once before reaching Bletchley, which is the last stop before Milton Keynes. This train gets there in good time, and it's a pretty ride out there.

Bletchley Park is literally across the street from the Bletchley railway station. It was constructed by the UK crypto department on the grounds of a typically flamboyant Victorian-era mansion that had been purchased by Naval Intelligence at the onset of the war. It is organized into "blocks," many of which are groupings of "huts." Some of the huts look like the name suggests, while others can be substantial brick buildings.

One walks up a long path past vintage-looking barbed-wire fences to B Block, a former center for decryption of Italian and Japanese traffic.  The beam antenna on top is for amateur radio. Upstairs are three operating positions with an interesting mix of vintage and modern gear. These will be replaced by an RSGB "National Amateur Radio Centre" which is under construction nearby.

This is where the self-guided audio tour starts. You pay your admission, watch an informative orientation film, and go through an absolutely first-rate collection of WW II cipher, crypto, and cryptanalysis machines. These are displayed alongside a rather quirky and interesting collection of all things 1940s, from product boxes and ration cards to vacuum cleaners and even metal toys.

Here is a striking reproduction of the radio room ("Funkraum") in a Nazi command bunker. Note the authentic vintage gear and the ENIGMA machine.

Moving on, we see a recreation of a typical Allied "Y-station" intercept position.  These were deployed in many places to capture enemy traffic for analysis and decryption/ decipherment at Bletchley. This combined COMINT effort considerably shortened WW II and maybe even turned the tide altogether.  Many, if not most, Y-stations used what "boat anchor" fans will immediately recognize as the National "HRO" receiver. From all the radios available, they picked the American HRO, with James Millen's indestructable tuning system.

We continue past many glass cases full of every imaginable WW II code machine, not to mention parts, tubes, and associated gear. One room is dominated by a megalithic black machine built like a bank vault and just as imposing.  This is the amazing Bombe recreation.

The original iteration of this electromechanical Godzilla was used to reverse-engineer the day's changing ENIGMA rotor and Stecker (plugboard) settings. This used a combination of brute force (each Bombe was equal to at least 36 ENIGMA machines) and operator insight to attack the ENIGMA cipher.  Bombes ground away 24/7 at Bletchley and other sites.  Operators used "cribs" (known or suspected plaintext), and other ideas to set the initial states for a run.  Successful solutions ("stops") would be tested on other machines until one worked. Then another round of ENIGMA enciphered traffic could be deciphered, usually the same day.

The Germans never lost faith in the ENIGMA machine, though they refined it as the war went on. Allies did not act on all intelligence, for fear the other side would catch on that its communications were no longer secure.  This sometimes caused heartbreaking decisions in which commanders knew that men would have to die.

After the war, all 200 or so existing Bombes were destroyed to keep the technology from falling into the wrong hands. It seemed like a good idea at the time.

The last photo in this set shows the extreme complexity of the Bombe's guts. Rebuilding one from scratch was NOT an easy task! 

All photos copyright © 2010 Hugh Stegman