Mark Brader:
> The disclaimer at the end of ["The Imitation Game"] describes it as
> "loosely" based on real events. That's certainly true...
> I'll provide more specifics in a separate posting that you can and
> should skip if you still want to see the movie.
Okay, here goes. Spoilers galore. And I'll repeat that despite
everything I say here, I still liked the movie somewhat.
[1] The boss.
Fiction: Turing and his boss Denniston are depicted in a cliched hostile
relationship, as if Denniston despises Turing for having a high assessment
of his own abilities and wants him to fail. Early on Turing goes around
Denniston's back and this increases the resentment.
Fact, by all accounts in the real world: That is not the way Bletchley
Park was run -- everyone *knew* they were on the same side, and while
the work was hard and the conditions dreary, the atmosphere was one
of collegiality.
Side point: Part of this hostility is because Turing was able to get
100,000 pounds allocated to develop the Bombe. In fact, once the device
proved itself, a large number of them were built and that amount was
the *total* cost.
[2] Cribs.
Fiction: 2 years into the war, a casual conversation gives Turing the
idea that it would be useful to guess some stereotyped text that might be
likely appear in a message. They try it out at once, and sure enough,
suddenly the Bombe produces the settings that enable them to decode
the message.
Fact: The *whole idea* of the Bombe, from the beginning, was to find
possible settings based on a guessed piece of text -- what they called a
"crib". Without that, it would just be spinning through all the possible
settings meaninglessly and there would be no way to tell when the right
one was found.
Side point: It wasn't as simple as "enter the crib into the machine,
start it, and read off the settings", either. But if they'd gotten the
basic idea right, *then* I think it would be reasonable for the rest to
be simplified.
[3] All at once.
Fiction: The movie makes it seem as though no German code was broken
until the Bombe was made to work, but when they did, that was all it took
and all messages could be read thereafter -- even though this leaves
it unexplained what all those people in the other huts were doing,
and where that first crib came from.
Fact: There were several separate German networks using Enigma, and
some of them (particularly the German navy) followed procedures more
carefully than others. If the machine was used carelessly, it wasn't
nearly as secure as the number of possible settings would imply, and
Bletchley Park took advantage. Some scenes show people using other
methods of codebreaking, without explanation.
Side point: The Bombes were designed to break Enigma machines with
three rotors, but in 1941 the German Navy began using 4-rotor machines.
For several months until the wiring of the 4th rotor was figured out
(through the events depicted in the book and movie "Enigma", and I won't
mention the entirely fictional "U-571" if you don't), this rendered the
codes unbreakable again.
[4] Midnight.
Fiction: Before the above happens, people are shown working feverishly to
break the day's Engima settings, but as soon as midnight strikes and they
have failed again, they give up because the settings will now be changed.
Fact: The faster a message can be decoded the better, but there is no
need to stop working on it just because the settings are out of date.
If you break the settings for one day, you can decode other messages
that you recorded on that day. Some of them may still be important in
themselves, and all of them may provide useful suggestions for cribs.
[5] No Colossus.
Fiction: Enigma was the only cipher machine the Germans used, even for
high-level communications from one regional headquarters to another.
Even the onscreen text at the end of the movie leaves this implication.
Fact: In about 1941 they introduced a number of still more sophisticated
machines that worked, not at the level of characters (converted to and
from Morse code by a human), but at the level of bits (in teleprinter
Baudot code). For the second half of the war one of these machines, the
Lorenz (code-named "Tunny" by the British), was used for all high-level
messages -- traffic far more important strategically than the messages
to individual units that continued to be Enigma-coded.
Bletchley Park had to start from scratch in dealing with these,
but they were able to break them too. To do it, they moved beyond
electromechanical machines like the Bombe to purely electronic machines --
the Heath Robinson and then the Colossus. And while Turing was not
one of the people responsible for these machines being built (the star
developer of the electronics was Tommy Flowers), Turing did produce
one of the first important recommendations for what they should do,
so this is part of his story too.
I can accept that the movie is not about the time period when the Colossus
machines were built, but pretending it never happened is another matter.
[6] Secrecy (during).
Fiction: When Turing and his group first broke a message with the Bombe,
Turing then realized that they mustn't tell anyone what it said, because
then the enemy would know what they were doing.
Fact: This was understood all along. It wasn't the codebreakers' job
to decide what to do with the information they decoded; that was for
people in a position to decide how it could be disguised as coming from
other sources. (Much of Bletchley Park worked on a need-to-know basis,
for good reason. Cryptographers knew how to break messages; they didn't
need to know what to do with the information, and they knew that.)
Side comment: There is a story to the effect that Bletchley Park
discovered that Coventry was to be attacked and Churchill himself chose to
suppress the information. In fact the message regarding Coventry simply
was not decoded and understood (Coventry was referred to by a code name)
in time for action to be taken. But when it was realized from Enigma
messages that a later attack in the series would be on Wolverhampton,
additional defenses were rushed to the site -- and seen by German
reconnaissance, leading to that raid being canceled.
[7] Secrecy (after).
Fiction: The onscreen text at the end of the movie says that the secrets
of Bletchley Park were kept for 50 years.
Fact: Some were, but many important secrets were made public only about
30 years later.
Side comment: Both Heath Robinson and Colossus used long loops of paper
tapes, running at unprecedentedly high speeds, as a form of external
memory. In about 1975 when I was at university, I went to a talk once
where pictures of one of these machines were shown and some of their
capabilities were explained, but when the speaker was asked what data
was on the tapes, he merely said "Ah!"
I wish I remembered how that speaker was, but at the time his name was
unknown to me. One obvious possibility is Bill Tutte, who played a major
role in the breaking of Tunny and was a distinguished professor there
at the time, I think Jack Good also spent some time at the university
and he was also on the project, so it could have been him.
[8] General-purpose computers.
Fiction: It isn't stated explicitly, but it seems to be implied,
that the Bombe is some sort of general-purpose computer, a successor
to Turing's purely theoretical concept of a universal Turing machine.
In a scene after the war he is working on some sort of general-purpose
electronic computer and it seemed to be intended to say that this
was a development from his Bletchley Park work.
Fact: The Bombe was a special-purpose device. Even the Colossus was a
special-purpose device, though it is is considered the first electronic
computer by people who like the idea that it was the British developed
the first electronic computer. What it did do was introduce techniques
that could easily *have been used next* to develop an electronic
general-purpose computer -- if only they hadn't been suppressed under
a veil of secrecy (just like the Bombes, as correctly depicted at the
end of the movie).
The British did eventually start a computer industry after the war,
and Turing did work on one of the early projects -- as did Flowers.
That work could be considered conceptually similar to the universal
Turing machine, but it did not flow from what was done at Bletchley.
[9] Soviet spies and Turing's exposure.
Fiction: There was a Soviet agent in Turing's group, who believed
that since the Soviets were British allies the British shouldn't be
keeping secrets from them. When Turing reported a minor theft, he was
investigated for possibly being that agent and thus a security risk.
The police investigated and instead discovered that he was homosexual,
for which he was arrested.
Fact: There was a Soviet agent at Bletchley Park, but not in Turing's
group, and he wasn't even suspected at the time. When Turing reported
a minor theft, he mentioned being in a homosexual relationship with the
probable culprit (on the assumption that this was unimportant), and was
therefore arrested (exactly as depicted in "Breaking the Code").
--
Mark Brader "Those who do not study history
Toronto are condemned to repeat the course"
m...@vex.net (after George Santayana)