May 3, 2012

The shooting party

Having briefly reviewed the contributions made by the Polish cryptographers and French intelligence service to the cracking of German military codes yesterday – and let us reiterate how very important both were – we can move on to the stars of both fiction and non-fiction, the codebreakers of Bletchley Park.

Bletchley Manor. Photo by Matt Crypto

Bletchley was a backwater with no significant military targets, a distinct advantage for the GC&CS, the so-called Government Code and Cypher School.  Bletchley Manor was within walking distance of the train station and the train itself connected to the line that ran between Oxford and Cambridge, the chief sources of cryptanalysts.

The Manor had been built by a Victorian financier, but by the 1930s it had seen better days and was scheduled for demolition.  At that point, in 1938, the head of MI6, Sir Hugh Sinclair, bought it and the first cohort of codebreakers and administrators moved in.

As cover, the earliest arrivals announced themselves as ‘Captain Ridley’s shooting party.’

One year later, the French provided the manuals and key lists for the Enigma machine and Polish mathematicians provided the formulae for decryption.

From 500 people at the start of the war, Bletchley grew to number 9,000 by the end; about 80% of those were women, mostly Wrens and Waafs.

On day one, staff signed the Official Secrets Act – GC&CS members did not talk about their work to friends or family. Or each other. The rules were
Do not talk at meals …
Do not talk in the transport …
Do not talk travelling …
Do not talk in the billet …
Do not talk by your own fireside …
Be careful even in your Hut …

People who worked at Bletchley did not mention it to their families until some 30 years after the war. Even today,  many refuse to discuss the details.

And no action based on code-cracking was ever taken without a red herring provided as a source of intel – in most cases a reconnaissance plane was sent out.  For obvious reasons, it was critical that the Germans never suspect that the Allies were reading their signals.

Less obviously, ‘Both of the two German electro-mechanical rotor-machines whose signals were decrypted at Bletchley Park, Enigma and the Lorenz Cipher, were virtually unbreakable if properly used. It was poor operational procedures and sloppy operator behaviour that allowed the GC&CS cryptanalysts to find ways to read them.’

In short, without human error, there’d have been no intel – and no way to track down the U-boats in the Atlantic, no way to stop Rommel at Tobruk.

No one had ever seen the Lorenz cipher teleprinter, but analysts reverse-engineered one from the logic of its signals  – the Colossus. The world’s first programmable digital electronic computer, it worked.

If you would like to know all the details about Bletchley, you can read about it in Harry Hinsley’s Codebreakers: The Inside Story of Bletchley Park or Britain’s Secret War by Michael Smith, or any number of other publications.  Just check the bibliography  here.

But you can also  listen to actual codebreakers describe life at Bletchely via interviews at a recent Bletchley gathering:

Sir Arthur Bonsall describes how he was recruited, the delightful Margaret Francis tells the story of how it was that her husband – serving in Italy – was actually the recipient of her signals, though neither knew it at the time, and finally, Giles Sandeman-Allen talks about his grandfather, mother and aunt, all of whom were at Bletchley in various jobs.

There are more interviews at the site – look in the column on the right.  What a joy to hear the actual participants describe history.



  1. A fascinating chapter in the history of IT. Thanks for reminding us of it.

    Comment by Jane — May 3, 2012 @ 5:56 am | Reply

  2. Love the blog good story and true, thank you.

    Comment by avery zia — May 3, 2012 @ 9:11 am | Reply

  3. I say old bean – absolutely super two blogs. Makes you wonder what if … ? Loved the bit about the magician who was a master expert at making pretend tanks, etc.

    Comment by Carol — May 4, 2012 @ 3:28 pm | Reply

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