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When the Japanese Foreign Office cypher machine, Purple, was broken by a
team from the US Army's SIS, several problems arose. Who would get the decrypts, which decrypts, how often, and under what
circumstances.
A logically prior problem, given inter-Service rivalries, was who would do the delivering. Both the Navy and the Army were
insistent that they handle all decrypted traffic delivery, especially to highly placed policy makers in the US Government.
Eventually, after much toing and froing, a compromise was reached. The Army would be responsible for the decrypts on one day, and
the Navy the next.
The distribution list eventually included some -- but not all -- military intelligence leaders in Washington and elsewhere,
some -- but again not all -- civilian policy leaders in Washington. The eventual routine for distribution included the following
steps:
- the duty officer (Army or Navy, depending on the day) would decide which decrypts were significant or interesting enough to
distribute
- they would be collected, locked into a briefcase, and turned over to a relatively junior officer (not always cleared to
actually see the decrypts!) who would 'make the rounds' to the appropriate offices.
- no copies of any decrypts were left with anyone on the list. The receipient would be allowed to read the translated decrypt,
in the presence of the distributing officer, and was required to return it immediately upon finishing. Before the beginning of the second week in December 1941, that was the
last time anyone on the list saw that particular decrypt.
There were several prior steps needed before any decrypt was ready for distribution.
- First, it had to be intercepted. The Japanese Foreign Office used both wireless transmission and cables to communicate with
its off shore units. Wireless transmission was intercepted (if it was possible to do so) and any of several listening stations
(Hawaii, Guam, Bainbridge Island in Washington
State, etc) and the raw cypher groups forwarded to Washington. Eventually, there were decryption stations (ie, including a copy
of the Army's Purple machine) in the Philippines as well. Cable traffic was (for many years before late 1941) collected at cable
company offices by a military officer who made copies and started them to Washington. Cable traffic in Hawaii was not
interecepted (illegality remember) until David Sarnoff of RCA agreed to allow it during a visit to Hawaii the first week of
December 1941. At one point, intercepts were being mailed to (Army or Navy) Intelligence from the field!
- Second, the raw intercept had to be decyphered. This was done by either the Army or the Navy (depending on the day) and,
because of the nature of the cypher and the break into it, was usually successful.
- Third, having obtained the plaintext, in Latin letters (!), it was translated. Because the Navy had more Japanese speaking
officers, much of the translating burden fell onto the Navy. And because Japanese is a difficult language, leaving much meaning
to context, effective translation required not only fluent Japanese, but considerable knowledge of the context within which the
message was sent.
- Fourth, the now translated decrypt had to be evaluated for its intelligence content. For example, is the ostensible content
of the message meaningful? If it is, for instance, part of a power contest within the Foreign Office or some other part of the
Japanese government, its meaning/implications would be quite different than if it were a simple informational or instructional
message to an Embassy. Or, might it be another message in a series whose meaning, taken together, is more than the meaning of any
individual message. Thus, the forteenth message to an Embassy instructing that Embassy to instruct Japanese merchant ships
calling at that country to return to home waters before, say, the end of November would be more significant than a single such
message meant for a single ship or port. Only after having evaluated a translated decrypt for its intelligence value could anyone
decide whether it deserved to be distributed.
In the period before the attack on Pearl Harbor, the material was handled awkwardly and inefficiently, and was distributed
even more awkwardly. Nevertheless, the extraordinary experience of reading a foreign government's most closely held
communications, sometimes even before the intended recipient, was astonishing. It was so astonishing, that someone (possibly
President Roosevelt) called it magic. The name stuck.
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