CODEBREAKERS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP84-00499R000500080004-0
• Release Decision: RIPPUB
• Original Classification: T
• Document Page Count: 4
• Document Creation Date: December 16, 2016
• Document Release Date: November 26, 2004
• Sequence Number: 4
• Publication Date: September 27, 1944
• Content Type: MISC

Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
Available
Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
 ILLEGIB Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
 Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
606 THE CODEBREAKERS
yang my best to make plain to you that this letter is being addressed to you
,o..;iy on my initiative, Admiral King having been consulted only after the letter
was drafted, and I am persisting in the matter because the military hazards
involved are so serious that I feel some action is necessary to protect the interests
of our armed forces.
I should have much preferred to talk to you in person but I could not devise
a method that would not be subject to press and radio reactions .s to why the
Chief of StalT of the Army would be seeking an interview with you t this par-
ticular moment. Therefore I have turned to the method of this letter, with which
Adm;cal King concurs, to be delivered by hand to you by Colonel Clarke, who,
incidentally, has charge of the most secret documents of the War and Navy
Departments.
In brief, the military dilemma is this:
The most vital evidence in the Pearl Harbor matter consists of our intercepts
of the Japanese diplomatic communications. Over a period of years our crypto-
graph people analyzed the character of the machine the Japanese were using for
encoding their diplomatic messages. Based on this a corresponding machine was
built by us which deciphers their messages. Therefore, we possessed a wealth of
information regarding their moves in the Pacific, which in turn was furnished
the State Department-rather than as is popularly supposed, the State Depart-
ment providing us with the information-but which unfortunately made o
reference whatever to intentions toward Hawaii until the last message before
December 7th, which did not reach our, hands until the following day,
December 8th,*
Now the point to the present dilemma is that we have gone ahead with this
business of deciphering their codes until we possess other codes, German as well
as Japanese, but our main basis of information regarding Hitler's intentions in
Europe is obtained from Baron Oshima's messages from Berlin reporting his
interviews with Hitler and other officials to the Japanese Government. These are
still in the codes involved in the Pearl Harbor events.
To explain further the critical nature of this set-up which would be wiped out
almost in an instant if the least suspicion were aroused regarding it, the battle
of the Coral Sea was based on deciphered messages and therefore our few ships
were in the right place at the right time. Further, we were able to concentrate
our limited forces to meet their naval advance on Midway when otherwise we
almost certainly would have been some 3,000 miles out of place. We had full
information of the strength of their forces in that advance and also of the smaller
force directed against the Aleutians which finally landed troops on Attu and
Kiska.
Operations in the Pacific are largely guided by the information we obtain of
Japanese deployments. We know their strength in various garrisons, the rations
and other stores continuing available to them, and what is of vast importance,
we check their fleet movements and the movements of their convoys. The heavy
losses reported from time to time which they sustain by reason of our submarine
action, largely result from the fact that we know the sailing dates and routes of
their convoys and can notify our submarines to lie in wait at' the proper points.
* Actually December' 11. Marshall was referring to Yoshikawa's message of
December 3, Honolulu to Tokyo, setting up Kuhn's signalling system.
T
Man
ofJa
attar
the
Ger
refe
pea
imf
peo
Em
cod
we
so u
is i
oil]
off
to
the
Pa,
ob
any
op
clc
po
TI
the J;
they
his ca
count
many
calla
his p,
ofav
the F
Approved For Release 2004/12/22 CIA-RDP84-00499R000500080004-0
 Approved For Release 2004/12/22 : CIA-RDP84-00499R000500080004-0
The current raids by Admiral 1-lalsey's carrier forces on Japanese shipping in
Manila Bay and elsewhere were largely based in timing on the knpvviWnovcments
of Japanese convoys, two of which were caught, as anticipated, irr'us destructive
attacks.
You will understand from the foregoing the utterly tragic consequences if
the present political debates regarding Pearl Harbor disclose to the enemy,
German or Jai), any suspicion of the vital sources of inforniatior. we possess.
The Roberts' report on Pearl Harbor had to have withdrawn from it all
reference to this highly secret matter, therefore in portions it necessarily ap-
peared incomplete. The same reason which dictated that course is even more
important today because our sources have been greatly elaborated.
As another example of the delicacy of the situation, some of Donovan's
people (the OSS) without telling us, instituted a secret search of the Japanese
Embassy offices in Portugal. As a result the entire milita y attache Japanese
code all over the world was changed, and though this occurred over a' year ago,
vy~z llaye nqt ct been, a.Ug.Lo-br ak thq new code, nd have thus lost this invaluable
source of information, particularly regarding the European situation.
A further most serious embarrassment is the fact that the British government
is involved concerning its most secret sources of information, regarding which
only the Prime Minister, the Chiefs of Staff' and a very limited number of other
officials have knowledge.
A recent speech in Congress by Representative Harness would clearly suggest
to the Japanese that we have been reading their codes, though Mr. Harness and
the American public would probably not draw any such conclusion.
The conduct of General Eisenhower's campaign and of all operations in the
Pacific are closely related in conception and timing to the information we secretly
obtain through these intercepted codes. They contribute greatly to the victory
and tremendously to the saving in American lives, both in the conduct of current
operations and in looking towards the early termination of the war.
I am presenting this matter to you in the hope that you will see your way
clear to avoid the tragic results with which we are now threatened in the present
political campaign.
Please return this letter by bearer. I will hold it in my most secret file subject
to your reference should you so desire.
Faithfully yours,
(Sgd) G. C. MARSHALL.
This extraordinary missive put Dewey in a grave predicament, He felt that
the Japanese simply could not be using the same code in Septemlber, 1944, as
they had been in November, 1941. Profoundly convinced of the rightness of
his cause and of the "dreadful incompetence" of the Democrats, both in the
country and the world as a whole and at Pearl Harbor in particular, he-and
many Republicans-might well have thought that true patriotism actually
called for exposing some three-year-old secret about prewar codes to prove
his point and elect the right man and the right party to control the destinies
of a whole nation. For with that exposure furnishing apparently solid evidence,
the Pearl Harbor charge might have propelled him into the White House.
Approved For Release 2004/12/22 CIA-RDP84-00499R000500080004-0