imitation game movie

[Pete Turnbull]

On 10/02/2015 05:21, Jon Elson wrote:
> There certainly were some real howlers in there, like the bit where Turing
> single handedly decides what info they would share with the British
> government, so as not to alert the Nazis that the Enigma code was
> broken!

I've not seen it but there's been a lot of criticism about historical 
(in)accuracy.

> Also, there is only one instance of the Bombe, while it is pretty well
> known they had a set of 350 of them at Ft. Meade running 24 hours
> a day.  And those were the NCR Bombes, running at 1800 RPM, insted
> of the one in the movie going clunk-clunk-clunk.  Some other papers
> seem to indicate there were another 350 Bombes at Bletchley.

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).

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.

> 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.

> Also, they have Turing building the Bombe with his own hands. Various
> descriptions have hundreds of people at Bletchley wiring the rotors and
> doing much of the other work.  The Bombe parts must have been made
> in machine shops across England.

All made by the British Tabulating Machine Company (BTM), though they 
subcontracted some parts.

-- 
Pete

-- 
Pete

Pete Turnbull