British provision of German naval Enigma information

Phil Jacobsen k6fw at
Tue Aug 29 01:15:11 EDT 2000

Ralph Erskine wrote:
> At 06:07 24/08/00 -0700, Philip H. Jacobsen wrote, in relation to the
> forthcoming (8 September) "The Emperor's Codes" by Michael Smith-
> >... This brings up the question whether the British responses to the
> >American gifts of Purple and Red cipher machines etc. in January
> >1940 was a fair exchange.  The written agreement setting up the
> >exchange has never been found or described in detail.  Also, the
> >exact list of what was supplied to the British and what was given
> >in return is still hotly debated.  Clearly, Purple and Red cipher
> >machines and other codebreaking data were given to the British.
> >A number of high level US Navy officers at the time were convinced
> >the British reneged on the deal while apparently the British view
> >was that the exchange was fair considering the situation at the
> >time.  Some new information from Kew reportedly indicates that
> >more information was provided by the British than previously
> >thought. ...
>>>> Although there have been claims of an actual agreement in late 1940 (or
> January 1941) to exchange cryptanalytical information, from the Public
> Record Office files it would appear that there was no such agreement. Thus
> on 22 November 1940, Brigadier Stewart Menzies ("C", and the Director of
> GCCS) wrote to the British Directors of Intelligence-
> "I am in placed in some difficulty, as the question of a full interchange
> [of cryptographic material] on Germany and Italy cannot be entertained at
> this stage" ... "when the [American] expert arrives, steps will be taken to
> steer him away from our most secret subjects" ... "the matter has been
> discussed with Sir A. Cadogan, who concurs that we cannot possibly divulge
> our innermost secrets at this stage, but that if the Americans return to
> the charge, it might be necessary to refer the question of policy to the
> Prime Minister".>>>>>>>>

See "The Ultra-Magic Deals" by Bradley F. Smith p. 53 for the Stimson
diary entries for November 1940 that confirm there was a "record of
the arrangement which was made."

As to the Menzies/GCCS letter, I note the word "full" before exchange.
Without more, it could be interpreted as an evasion of a previous
agreement for a "full" exchange.  From an account by Prescott Currier,
one could surmise that Cadogan did his minor part in keeping the
mission occupied.  The next issue brought up could fall nicely into
that possible scenario.

>>> Any agreement would clearly have required Churchill's approval. All the
> indications are that he was first approached in this area by Menzies on 26
> February 1941, when he was asked for permission to show the British bombes
> (fast Enigma key-finding aids) to the members of the Sinkov Mission (which
> brought Purple clones for GCCS).>>>>>>>>>>>>>>>

There are numerous examples of President Roosevelt agreeing to secret
matters verbally and not making any written record of such agreement.
Many high ranking officers acted on such verbal agreements.  I would
expect there were many similar situations with Churchill.

The request for the Sinkov group to be allowed to see a Bombe could
have come from a previous decision not to provide a "full" exchange
of their major cryptanalytic successes despite an agreement to the
contrary.  When they saw the bounty they received from the American's,
it is possible someone's conscience bothered them and suggested the
Americans in return be shown the Bombe.  Up until very recently,
the record was clear that the Sinkov Mission had not been shown a
On the American's side this was denied and as far as I can tell no
one has suggested that any details of the British Bombe were provided
at this time.

>>> If there was an agreement before the Sinkov Mission arrived, why were the
> two naval members (Lt Weeks and Ensign Currier) not briefed about it, so
> that they could know what to expect in exchange for the Purple clones etc?

I doubt a one page agreement listed specifically what was to be given
by each side in the exchange but other references suggest each side
was to give "all" of its important successes or secrets on German,
Italian and Japanese cryptanalysis.

When you look a the relative low ranks on the American side, it seems
most plausible that they were primarily "couriers" is deliver what
the US Army and US Navy decided would fulfill their obligations
under the agreement and were also "couriers" to bring back whatever
the British decided met their obligations under the agreement.
They were also told to keep their eyes and ears open and Sinkov
and Currier took notes.  Even though the agreement probably did not
spell out specifically what each side would provide, each side knew
generally which codes and ciphers the other had success with so
they were willing to make an exchange with a generalized expectation
of what they would get in return.  The British knew we had solved
Purple and Red and the Americans knew the British had made great
strides on the German Enigma.  The British had the advantage as
the American contributions were opened up first as I recall and the
British response could have been adjusted downward if desirable.
However, when they saw what bounty the American's brought, possibly
someone may have been of a mind to add a viewing of a Bombe.  Until
recently it was universally thought that such a viewing was denied.
Also, it was the British pattern for almost the next two years to be
reluctant to part with "all" of their secrets.

Safford, and others have given their views as to what was in the
agreement.  Since Safford had to gather the US Navy's contribution to
the agreement, he was in a position to know its particulars.  He
would also know that the Army was going to part with the Purple
cipher machine.

> Commander L Safford claimed after the war that, in particular, the British
> reneged on an agreement, and that the Sinkov mission came back empty
> handed. But Safford was writing around 1950, and was clearly wrong, since a
> 1942 memo that he wrote (and oral evidence from Weeks and Currier) shows
> that the British supplied the naval members (at least) with a "paper"
> Enigma (the wiring of its rotors). They also gave OP-20-G more information
> about Enigma in the fall of 1941.>>>>>>>>>>>>>>

Since the US Army had a commercial model of the Enigma available,
the "paper Enigma" now reported to have been given to the Americans
have been of some immediate use to the Army.  However, it is apparent
OP-20-G files whatever was given on Enigma only generated many more
questions as to how it actually operated.  An actual Enigma clone would
have easily shown how it actually operated.

> Admiral Noyes (the USN Director of Naval Communications) thought that GCCS
> had broken an agreement to supply intelligence (Ultra) from naval Enigma -
> (and various codebooks). The PRO files indicate clearly that the British
> did not agree to supply all naval Ultra in 1941, although they did send
> some, in relation to the Atlantic. That part of the dispute seems to have
> blown over in early 1942.
> As to what the Mission received from GCCS, see "What did the Sinkov
> Mission Receive from Bletchley Park?", Cryptologia, 24/2 (2000) 97.>>>>>>

The new allegation repeated on p. 98 of the above article that the
Sinkov Mission was shown a British Bombe is quite startling especially
since it contradicts prior information from Sinkov, Rowlett, and Currier
or even British sources.  One would think that the memory or notes of
the Americans would have contained this earth shaking revelation.

In evaluating the exchange of January 1941, one might harken back to
to 25 and 26 July 1939 where Commander Dennison, Alfred Knox and
Stuart Menzies were shown all of the Polish hardware and software
including the Zygalski sheets and the simpler Polish Bombe.  The
Poles went even much further giving the British (and French) a copy
of the Enigma cipher machine, built in Poland, together with the
drawings and plans of the Bombes and perforated sheets.  All of
this was given for the mere expectation that the British (and the
French) would produce the necessary larger Bombe now needed for
the increased security measures used by the Germans for their
Enigma machines.  However, when the Americans came with their
"gifts" including a Purple machine (and the one destined for Pearl
Harbor or more to follow), they received no Enigma machine, not
even the one the Poles gave them, and no drawings or plans for a
Bombe at the very least.

The only reason to revisit this exchange and the British reluctance
to provide "all" of their Enigma secrets until late 1942 is due
to Michael Smith's allegation in "The Emperor's Codes" that the
British had been willing to provide the Americans with all they
gained from breaking the Enigma.  If one or a few OP-20-G high
ranking officers were, in fact, hesitant to provide "all" the
Japanese naval technical information on security grounds, such
actions could find their genesis in earlier British reluctance
for the same reasons.

Philip H. Jacobsen

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