imitation game movie

Jon Elson elson at
Tue Feb 10 11:37:25 CST 2015

On 02/10/2015 09:29 AM, Pete Turnbull wrote:
> I'm not an expert, but I think you're a bit wide of the 
> mark in places.  You're evidently referring to the US Navy 
> bombes. Although the original contract was apparently for 
> 350, only 121 were ever built, including prototypes, and 
> they were used at the US Navy Communications Annex in 
> Washington, not Ft Meade.  The US Army also had a small 
> number of bombes built closer to a British design.  And 
> the reproduction at Bletchley doesn't run at the full 
> speed of the later British ones, although it's true the US 
> Navy Bombe was a good deal faster (850rpm or 1725rpm vs 
> 120rpm; various sources suggest between 5 and 10 times 
> faster in practice).
There is a 7-part article about the building of the NCR 
Bombes that I read.  It was written largely
by Joe Desch's daughter.  He was the main designer and 
project leader of the NCR Bombe.
It is an interesting story, but I have failed to find the 
link again in a quick look.  Possibly the 350 number
was the number originally ordered, and she found this number 
in documents, but didn't
know that the production was cut short as the machines were 
so successful.
> Bletchley itself had only a small number of bombes.  Most 
> of the 224 built in Britain were housed at outstations.
> Because I've not seen the film, I don't know what the 
> "clunk-clunk-clunk" you refer to is, but I've seen and 
> heard the bombe running and I would bet it's the sound of 
> the middle wheels advancing, roughly once a second on the 
> replica, but faster on most of the British bombes.
Yes, exactly.
>> It only makes sense for there to be a big array of NCR 
>> Bombes, not
>> the slow British-built ones, but
>> with all the ships being sunk, how could they be sure 
>> such a shipment
>> could make it across the Atlantic?
> They didn't.  No bombes were ever shipped across the 
> Atlantic. Only design drawings and information were, in 
> the care of officers from the US Army and Navy in 1941, 
> and later two USN and some senior Bletchley staff in 
> 1942.  The US Navy bombe was an adaptation of the British 
> design from the latter exchange, and went into service in 
> 1943.  Britain had been using their bombes for several 
> years by then, of course.
> Bletchley apparently did use USN bombes, but not 
> directly.  They did it by sending cribs and getting the 
> stops and settings back over encrypted cable, to be used 
> for decryption of 4-rotor Naval Enigma messages at 
> Bletchley Park.
Yes, this is as I suspected, due to the difficulty of 
sending anything across the Atlantic, and the
EXTREME sensitivity of the project.  They actually did a LOT 
better at keeping this one
secret than they did with the Manhattan project.


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