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FRIENDS AND ALLIES
41
*
The talk then turned again on the question of security. They
wanted to know whether my despatches went by radio or
cable and were relieved to hear that they went by cable,
and were further relieved to hear that we have a direct
wire straight into the War Department. However, I pointed
out that this wire was subject to interception by their people
here in England [GC&CS] and I had no doubt they had
taken our messages and attempted to decipher them.
*
He added that it was now very much in the interests of GC&CS
to be honest about the :;ecurity of American cypher systems,
'because the stuff that is going over it is more vital to them
than to us'. Lee's frank exchange with the British underlines
one of the hidden benefits of cooperation between the Allied
code-breakers. Once they began to share their most precious
assets, 'Magic' and then eventually Ultra, improved communications
security became paramount. London and Washington
now had a vested interest in the impenetrability of each other's
messages. After all, if GC&CS could break American codes, then
so, perhaps, could the Germans.43
Churchill eventually wrote to Roosevelt and owned up to British
work on American diplomatic codes. 'From the moment we became
allies: he explained, 'I gave instructions that this work should
cease. However, danger of our enemies having achieved a measure
of success cannot, I am advised, be dismissed: In fact, it is unlikely
that all work on American traffic ceased. In areas such as the
Middle East, Britain had a considerable incentive to continue to
work on American commercial traffic, much of which was in
commercial code or plain text. Indeed, a close reading of Churchill's
assurance to Roosevelt suggests that it might have related to diplomatic
traffic only.44 Some GC&CS staff recall work on the traffic
of American commercial attaches throughout the war, although
as yet no documents have been released. 45 Predictably, clear traffic
from American oil companies was being intercepted in 1944 as
they began to look for new markets in Europe.46