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Authors: Michael Smith
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the ‘entry plate’ in the
Wehrmacht
’s plugboard machine. Given the enormous number of different permutations available to the Germans, Foss and Knox had not imagined that it might simply
be in alphabetical order. This was probably the most important single piece of information that the Poles provided.
MS
My earliest recollections of the Enigma date back to 1926. We then knew of two models: large typing [B model] and small index [C model], I never saw the large machine and don’t know if it was ever widely used. It was the small index model that was later developed and used by German services and others.
It will be best to dispose of the large Enigma in a few paragraphs to avoid confusion. Its UK patent specification was 231,502, application date 25 March 1925, convention date (Germany) 25 March 1924. A letter from the Aeronautical Committee of Guarantee, Berlin, to the Air Ministry, dated 19 June 1924, said: ‘The invention, in an incomplete state, was examined in about 1921 by Lieutenant Hume, Office of the Military Attaché, British Embassy, Berlin, and it is believed, an expert was sent out from the War Office.’
[A letter from] Hume to [Edward] Travis, 29 July 1926, says that the company have informed him that they have sold out all the big machines and no more of this pattern will be manufactured. An improved model may be ready in 10 months’ time. Perhaps the Admiralty would meanwhile like to buy a model of the small machine. The improved model of the large machine was on view in 1928.
There is a brochure in French ‘
La Machine à Chiffrer, Enigma’
issued by
Chiffriermaschinen Aktiengesellschaft
, Berlin W, 35 (undated, but presumed about 1924). This deals with the machine from the user’s point of view and gives no details (apart from the usual astronomical number of key variations) of the ciphering. There is also a brochure in German.
An undated report describes a demonstration of the large machine at the Foreign Office on 27 March (possibly 1926). It was a typewriting model (called the ‘Typing Machine’ as opposed to the small ‘Index’ machine) and worked from the main current (DC). It had previously been demonstrated in Stockholm. It was a one-way machine (i.e. it had no reflector wheel), with four drums which were moved by four ‘gap-tooth’ cog wheels with different numbers of teeth on each, some of the teeth being operative and others not.
Sometime in 1927 or so Travis gave me a small machine to examine. I was not told where it came from, but presumed it had been boughtas a sample. This was the Enigma referred to [in the GC&CS history]
German Abwehr Cryptographic Systems and their Solution
vol. 1
(The Unsteckered Enigma).
A worker [Keith Batey] on the SD (
Sicherheitsdienst
) Enigma having recovered the upright, the next most natural step to take was to see whether any known machine had a wheel defined by this upright. This led to a most surprising discovery: that the wheel recovered was identical with wheel I of a certain commercial machine said to have been purchased by Mr [Dilly] Knox in Vienna in 1925. It had in fact been lying in a cupboard behind the person who made the original break.
The only difference between the two machines was that the turnover notch had been transferred to the tyre [ring] [in the SD machine]. I don’t know when this model [the small (Index) machine] was first made. It had movable tyres but the turnover notch was on the wheel and not on the tyre. Incidentally, the Air Ministry used this model as an inspiration for Typex * which also had turnover notches on the wheel and not on the tyres.
I wrote a paper entitled ‘The Reciprocal Enigma’ (the large Enigma was not reciprocal) in which I showed how, if the wiring was known, a crib of fifteen letters would give away the identity and setting of the right-hand wheel and how, if the wiring was unknown, a crib of 180 letters would give away the wiring of the right-hand and middle wheels. The methods I used
Wehrmacht
’s plugboard machine. Given the enormous number of different permutations available to the Germans, Foss and Knox had not imagined that it might simply
be in alphabetical order. This was probably the most important single piece of information that the Poles provided.
MS
My earliest recollections of the Enigma date back to 1926. We then knew of two models: large typing [B model] and small index [C model], I never saw the large machine and don’t know if it was ever widely used. It was the small index model that was later developed and used by German services and others.
It will be best to dispose of the large Enigma in a few paragraphs to avoid confusion. Its UK patent specification was 231,502, application date 25 March 1925, convention date (Germany) 25 March 1924. A letter from the Aeronautical Committee of Guarantee, Berlin, to the Air Ministry, dated 19 June 1924, said: ‘The invention, in an incomplete state, was examined in about 1921 by Lieutenant Hume, Office of the Military Attaché, British Embassy, Berlin, and it is believed, an expert was sent out from the War Office.’
[A letter from] Hume to [Edward] Travis, 29 July 1926, says that the company have informed him that they have sold out all the big machines and no more of this pattern will be manufactured. An improved model may be ready in 10 months’ time. Perhaps the Admiralty would meanwhile like to buy a model of the small machine. The improved model of the large machine was on view in 1928.
There is a brochure in French ‘
La Machine à Chiffrer, Enigma’
issued by
Chiffriermaschinen Aktiengesellschaft
, Berlin W, 35 (undated, but presumed about 1924). This deals with the machine from the user’s point of view and gives no details (apart from the usual astronomical number of key variations) of the ciphering. There is also a brochure in German.
An undated report describes a demonstration of the large machine at the Foreign Office on 27 March (possibly 1926). It was a typewriting model (called the ‘Typing Machine’ as opposed to the small ‘Index’ machine) and worked from the main current (DC). It had previously been demonstrated in Stockholm. It was a one-way machine (i.e. it had no reflector wheel), with four drums which were moved by four ‘gap-tooth’ cog wheels with different numbers of teeth on each, some of the teeth being operative and others not.
Sometime in 1927 or so Travis gave me a small machine to examine. I was not told where it came from, but presumed it had been boughtas a sample. This was the Enigma referred to [in the GC&CS history]
German Abwehr Cryptographic Systems and their Solution
vol. 1
(The Unsteckered Enigma).
A worker [Keith Batey] on the SD (
Sicherheitsdienst
) Enigma having recovered the upright, the next most natural step to take was to see whether any known machine had a wheel defined by this upright. This led to a most surprising discovery: that the wheel recovered was identical with wheel I of a certain commercial machine said to have been purchased by Mr [Dilly] Knox in Vienna in 1925. It had in fact been lying in a cupboard behind the person who made the original break.
The only difference between the two machines was that the turnover notch had been transferred to the tyre [ring] [in the SD machine]. I don’t know when this model [the small (Index) machine] was first made. It had movable tyres but the turnover notch was on the wheel and not on the tyre. Incidentally, the Air Ministry used this model as an inspiration for Typex * which also had turnover notches on the wheel and not on the tyres.
I wrote a paper entitled ‘The Reciprocal Enigma’ (the large Enigma was not reciprocal) in which I showed how, if the wiring was known, a crib of fifteen letters would give away the identity and setting of the right-hand wheel and how, if the wiring was unknown, a crib of 180 letters would give away the wiring of the right-hand and middle wheels. The methods I used
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