The Women of Bletchley Park

Really good article about the women who worked at Bletchley Park during World War II, breaking German Enigma-encrypted messages.

EDITED TO ADD (7/13): There's also a book: The Debs of Blechley Park and Other Stories, by Michael Smith.

Posted on June 29, 2017 at 12:40 PM • 16 Comments


Slime Mold with MustardJune 29, 2017 2:19 PM

If @Bruce had see the painfully bad television program "Bletchley Circle" he would have avoided the topic altogether.

Clive RobinsonJune 29, 2017 2:54 PM

From the article,

    Today, the mansion in the heart of the southeast English countryside

Not realy if you look at a map of England it's a good distance north north east of London on the south side of "the middlands".

On of the reasons it was picked is that the local railway station was a croising point in central England where there were trains to both Oxford and Cambridge. That area in general being fairly rural was ideal for not just the code braking but signals intercept and a whole load of other clandestine operations. In some respects it was also about "as far in land" as you could get, and the entire area was essentially flat with good ground conductivity in all directions which made it desirable for signals work.

CassandraJune 29, 2017 4:32 PM

I will block-quote, simply because I cannot précis the author's comments and links, from a posting on 'The Register' comments on an article (Thank-you Mr. Nescio):

While it is well known that the Poles, and subsequently the British 'cracked' Enigma, what is not so well known is that the Americans manufactured 120 (!!!) of the 'Bombes' and used them at the United States Naval Computing Machine Laboratory, Dayton Park, Ohio to decode Enigma-encrypted messages during the Atlantic (U-boat) war.

The enormous amount of resources the USA could deploy made a significant difference.

It's also instructive to read about the 'Tunny' code and the development of the Colossus; some information about which was not declassified until June 2000 in the UK. It's a long read, but well worth it if you are interested in the history of cryptanalysis and computing.

The Dayton Codebreaksers included many women, like Bletchley. There is more detail at the link. I also recommend the Rutherford Journal article - it is a very good read.

neighbor7June 29, 2017 8:07 PM

"Bletchley Circle" is definitely mediocre, but still fun in a certain undemanding frame of mind.

David RudlingJune 30, 2017 3:39 AM

"where the brilliant mathematician Alan Turing cracked the Nazi's Enigma code"
Oh, not again. No he didn't - the poles did. Dilly Knox came as close as anyone at Bletchley Park but not Turing. What Turing brilliantly did (with assistance from Gordon Welchman) was to turn a substantially manual process into an industrial scale operation so that vast quantities of traffic could be read. As was pointed out in the official history of Hut 6, it was the ability to synthesise information from many individual operational messages into comprehensive intelligence that made Ultra so valuable. So enormous credit is due to him for exploiting Enigma on an industrial scale but not for "cracking" it.

WillJune 30, 2017 7:10 AM

@David Rudling

Alan Turing did crack the enigma, e.g. inventing the eins catalog and Banburismus and the bombe. He was not alone. It wasn't like the movie. There are lots of others who also need credit and who don't get nearly enough lime-light. But I still think it accurate to say he "cracked the enigma" :)

The Poles cracked the pre-war Enigma, which was a massive intellectual feat. But the most important thing they did was show it could be broken. It is easy to speculate that without the Polish sharing their results, the allies would likely not have believed they could and would not have tried.

Martin PotterJune 30, 2017 8:00 AM

The Americans made a huge contribution to the cryptologic effort in WWII. But you have to remember that they only began in 1942; Britain and her allies had already been at war for almost 2-1/2 years and all the early successes were their's alone. As I recall, before 1942 Britain shared little knowledge of significance with the USA.

LPA-11KJune 30, 2017 8:27 AM

@Martin Potter

Technology transfer between the US and UK loosened up with the Tizard Mission towards the end of 1940. Among the things tabled included the cavity magnetron ("the most valuable cargo ever brought to our shores"), specs on the Chain Home radar system, the proximity fuse, and feasibility studies on the fission bomb. The Tizard Mission set a precedent making it politically easier to share cryptography methodologies after the US formally entered WWII.

In some book I have read in the past, the description of the bombe machines in operation told of smoke coming off the tape reels. I have booted PDP-11s and 8s with paper tape in the past and still marvel at how fast we can sling bits these days.

Clive RobinsonJune 30, 2017 8:59 AM

@ Will,

What held Dilly up was not knowing the order of the keyboard to rotors.

The Poles simply "Guessed at the German regimented mentality" and tried the simple A=1, B=2, ... and got it right first go.

As for the early enigma, it got broken fairly easily because it stepped the rotors from the wrong end. Although the British did have an attack method the French actually imoroved on it (see rod and cliques methods). And for all it's mechanics the enigma can still be tested or emulated by simple strips of paper three for the rotors and one for the stecker board.

Importantly the real secrets behind much of the breaking was the "Dockyard cipher" and the weather information and a catalogue combined later with traffic analysis.

The dockyard cipher was weak and the British went over and dropped a few mines etc (gardening) outside a German controled harbour knowing that a standard message would be sent out on both the dockyard cipher and the more secure kriegsmarine systems, thus a known plaintext could be obtained from the dockyard system to be used to attack the kriegsmarine system. Similar was done with weather messages and joint operations with the Italian's who's systems were weak.

But in the main the main way the enigma got broken was via probable plaintexts. The German's had a very regimented way of sending signals often starting with a well known name etc which was "circuit based" and they also tended to end with Heil Hitler". Huf Duf (HF DF) and later Traffic analysis gave the circuit or net information, which could be used to get names and other information from the catalogue of over 2million pieces of information kept on library "file cards" which gave probable plaintexts by which crib settings were obtained.

With out the catalogue which was started before day one of enigma breaking the majority of breaks would not have been possible.

There were also other weaknesses in the German keying systems that gave rise to the likes of "cillies" etc. Basically humans are both lazy and non random. It was observed that a key for a new message often was just a couple of rotor movments away from the last positions from the previous message sent/received. Further at turn around at midnight when the enigmas were reset up, if there was a rotor change, then the chances were the operator would have the ring setting values uppermost in the enigma and thus the first message sent would have keying informatio close to the ring setings more often than not.

But to make a point, it took Alan Turing several months to come up with the bomb idea. Gordon Welchman however did it independently from scratch in a few days. Further Gordon went on to design the all important diagonal board that when he described it left Alan and several others entirely speachless. Gordon also put in place the idea of Traffic Analysis and it later became the cause of his name becoming blackened by the UK Gov in the 1980's when Maggie Thatcher went on the war path against "leakers". Gordon wrote a book about his experiences in which he described the mechanics of Traffic Analysis. It turns out that although upset over Winterbotom's revelations in the early 1970's which caused some nations to stop using their old enigmas and similar US war surplus ciphers, the secret the British wanted kept hidden was Traffic Analysis.

Thus nolonger being a British Citizen Gordon wrote his book unaware of a couple of things, a secret agreement that was a follow on from the BRUSA agreement, that what the British decided was classified the NSA et al would respect as classified and the sensitivity over Traffic Analysis.

The result was he had his US security clearence revoked and the US IC then tried various tricks to bankrupt him...

It's a shame because other work that Gordon did was the fundemental work that gave us the Internet through Rand where he worked the DOD DARPA and Bolt, Beranek and Newman (BBN) in Cambridge, just up the Charels river from Boston, and MIT where the two B's were profs.

The US developement of bombs was a little unusual, theor design was based around relays, that although faster than the origanal British Turing bomb was nowhere near as fast as the later supper bombs required to break the four wheel enigma with a choice of eight rotors the Getman submarine enigmas became. Further late in the war was the Luftwaffe fourty position "Uhr box" which if it had been brought into service much earlier and in a more general way would probably have defeated the alied breaking of enigma entirely.

The whole history of the enigma was one of "riding the leading edge" the Germans were over confident in the system they had put together, and only slowly made incremental improvements. This alowed the Brirish to come up with improvments in their methods "only just in time" and aby one of them happening six months prior to the actual date it was introduced would have either killed or very servearly set back the ability to break the enigma as regularly as it was.

David RudlingJune 30, 2017 9:47 AM

@Clive Robinson
A very fair potted history.

I fully acknowledge that many people largely unknown outside the circle of enthusiasts and historians contributed to, one could say, keeping Enigma cracked open throughout the changes to it during the war. You and I both appreciate what an ongoing battle it was and that it was not a case of once cracked, always open. But I still maintain that the credit for the initial crack is due to Marian Rejewski and his team, not to Turing and my comment was related to that oft repeated inaccuracy. Turing deserves every credit for a fantastic achievement but let it be for the historically correct achievement not an inaccurate myth.

markJune 30, 2017 11:41 AM


Thank you very much for posting the link.

My late wife's mother was a war bride. To the end of her life, she got a small pension from the UK for her work during the War - she was drilling holes for rivets in the line manufacturing Spitfires during the Battle of Britain.

And I honor... or perhaps that should be honour, all that they did, and their memory.


BrianRJune 30, 2017 12:07 PM

I always consider Bletchley a good example of organisational skill, something the UK is not necessarily well known for these days. It's the organisation which is breathtaking as much as the technological breakthroughs.

Not sure it matters who broke Enigma, I'd go for the Poles as a rule with Turing et al carrying on the work. For the code breaking to work and be effective Bletchley (and the other sites) needed the benefits of numerous different skills on top of those of Turing, Newman, Tilte, Goode etc. It's daft to cherish a handful of names when 1000s deserve recognition.

If you're interested in WWII technology have a look at R V Jones' "Most Secret War", it definitely an interesting read.

DAvid RudlingJune 30, 2017 1:00 PM

Only just read your link to "A brief history of the Enigma and the pre-war cracking of it" which must have appeared while I was writing my first note. Very good piece.

CallMeLateForSupperJune 30, 2017 6:17 PM

There is a small-ish soft-cover book that is a compilation of of a dozen or more interviews of women who worked at Bletchley and intercept stations, Ruth Bourse among then, IIRC. It is well worth a read. Sorry, I don't remember the book's title, and I didn't find it on the shelf when I looked a few minutes ago.

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