L 

REF ID:A488117 

~xtracted from. CONQRESSIOHAL INVE;;TIGATIOR tF.A.RL HARBOR ATT.lCl, Part J, p. 1132-1133. 

/j.JS7J;.] 

For Mr. Dewey's eyes onl,y. 

"ffiopx.7 

'1'01' s:eem 

27 September 1944. 

"My dear ~overnorz Colonel Clarke, my messen~er to you of yesterday, September 2&th, h&s reported the r•ault or hie delivery ot my letter dated September 

25th. As l underetand hill you (a) were unwillin~ to cOIUlit yourself to 9.1\Y 

agreement regarding 'not com..~unicating its contente to any other person' in 

view of the fact that you felt 7ou already knew certain of the thlnga probably 

referred to in the letter, 1.8 suggested to you by seeing the word 1 eryptograph, 1 

and (b) you could not feel that such a letter as thb to 11 presidential candidate 

could 1·1s.ve been addressed to you by an officer in my position without the knowled~ 

of the i:re11ident. 

"As to (a) above I am qulte willing to have you read what comes hereafter 

""::.th the understandi;i,~ that you. a.re bound not to cornmunlcat.e to any other 

person &rl,1 portions on which you do not now lie.ve or later receive factual 

kn or.ledge from. some other source thart myself. As t~ (b) above you have my 

'l'ford that neither the Secretary of wor nor the Premident has an;r int.iaation 

wh~tsoever that such a letter has been addressed to you or the.t the preparation 

or sending of such a. communication was being considered. I aHure you that 

the only persona who saw or know or the existence o! either this letter or Fl1' 

letter to you dated September 25th are ACl:linLl. King, seven key otf icers reaponaible for security of military communications, and my secretar;r who typed 

these letters. I am trJing m1 beet to make plain to you th.at this letter ia bei111 

addressed to you 1olely on rrrr initiative, Admiral King having been consulted 

only after the letter was drafted, and I am persisting in the matter because the 

milltsry hazards involved are ao serious that I feel some aotion ia nece1sa:ry 

to protect the interests of our armed forces. 

•I should have much pre!erred to talk to you in person but I could not 

deviso a method that would not be subject to press and radio reactions as to why 

the Chief of Jtaff of the Arm7 would be seeking an i!'lterview with you at this partieular moment. Therefore I have turned to t~e method of this letter, with 

Declassified and approved for release by NSA on 11-06-2013 pursuant to E .0. 1352a 
-

REF ID:A488117 

COP I 

which Admiral King con.mrrs, to be deliver~ by hand to you by Colonel Clarke, 

who, incidentally, has charge of Vie most secret documents of the ·11s.r and Navy 

Departments. 

"In brief, the military dile1111a ls this; 

"The most vital evidence in the .rearl Harbor matter consist• ot our 

intercepts of the Japanese diplomatic oommunieation1. Over a period of yeara 

our crn.;tograph people analyzed the character of the uchine the Japanese were 

using for encoding their diplomatic meaasgea. Baaed on th!JI a eor:reaponding 

machine was built by ua which deciμhers their measagea. Therefore, we poHeased 

a wealth of information regardin,g their movea in the r'aelfic, which in turned was 

furnished the State De;artment--rat~er than as ia popularly supposed, the ~tate 

f2987f7 Depart,11ent :,rovidins- us with the inf orll4tion--but rL11ich u.nfortunutAly made no refeT"enca whatever to intentions toward Hawaii until the last 

messa;e before :::>ace1nber 7th, which did not reach our hands until the foll01rlng 

day, Gece~ber Stp. 

11 ~ow the point to the present dileia11.1t is that •• ha ff gone ahead with this 

"l:lusiness of deciphering their codes until we po11eas other codes, 1errnan ae nll 

as Japanese, but our main basis of inlol"llatlon regarding Hitler's intontions in 

Europe is obtained from Baron Oahima'a messages frOlll Derlin reporting his 

interviews with Hitler and other officiale to the Japanese Government. Theae 

are still in the codes involved in the pearl Harbor ev~nts. 

1

tTo explain further the critical nature of this aet-up which would be wiped 

out almost in s.n instant if the lea.at suspicion were aroused regarding it, the 

battle of the Coral sea waa baaed on deciphered meeaagea and therefore our few 

shipis w8re in tt'e right pl.ace at the right time. Further, we were able to concentrate our limited forces to meet their naval adYance on Midway when otherwise we almost certainly would have been aoaae J,000 mil.ea out of place. We 

had full information or the strength of their forces in that advance and alao of 

the smaller force directe-0 against the Aleutians which finally lsnded troops on 

Attu and Kiska. 

"Operations in the Pacific a.re large~ guided by the information we obtain of 

Japane1Se deployments. We knr)W their strength in various gar:risone, the rationa 

2 
-

REF ID:A488117 

c 0 .1 r 

and other •tores continuing available to them, and what i• ot TO.St btportanoe 

we Oh9Ck t.h"ir .f~eet move.aierit.• anti the movemente of their oomoys. '!he beav7 

loaees reported from tiIDe to time which t~ey sustain by reason of our submarine 

action, la.r:_;e.J.y result from the fact that. we know the &ailing <!at.ea anc routes of 

th(;li.r convoy» a11d can notif,1 our subma.rint>e to .1.ie in aa.it at the proper points. 

"The current ra.iua by Admiral ~lala\ty 1 a carrier furcea on Jat-aneae ehipμln~ 

1n ih&aila Bay and e.J..aclihero '1(n·e .Largely baaed 1n tiati:lt; on the known movementa 

of .Japanese c.:>nvo;rs, two of which "ere caught, ae snticlpated. in hia destructive 

at tac its. 

''l'.ou wiJ. ... 1 .. ul(J.ershnd. from the foret&Oillii the utlerly tragic conaeq11ences it 

the .i-'l'!J'sent f·Olltioal debates rei8f.rdinp, r earl !\arbor cbcloae to the •llell1t 

:Jt~r.:i.:ii.n or Jap, any auapicion of the vital sources of i!lfoneation we possees. 

1'1''.•e ?-.oberta 1 rsport on • oarl :1arbor had to [)a_ve "Aithc~ra'llr?'l fro!ll'I it a.U. 

ruferl')nce tv t!lh hiihl1 secret rnattel", tha-refore in portions 1t neeeai:.arily 

appeared incor~plote. The ~m~e reaaon w1: ich cl ictated t l-:at course le even 

.iore 1111portant tou'i;t b-ccause our sources have b~!':t~l ;;reatl;r ~J.aborated. 

11 fi.:r,117 AS anot 1

·;er eump.l.a of the delio~r of' the dt.uation, some at 

vono'l&•1'a peo;,:le (tbe OJ.3) without telling us, instHutfid u. secrot S;"!aroh of t>ie 

Japa.iese ~oossy offices 1n .tortu~lill. t .. 111 s. result the entire military attache 

Javanese co<le 111.J.. over the ~·orld was chan~~ed, a:lt- t·::ough t!:is occUl"re<.! over a 

year ago, we he.Te !lot yet been able to brerik the new cod• and have thus loat 

t.his. invaluable source of information, ps.:rticularl,y :re,iarding the European 

aitua.tion. 

"a furLlur moat serious embarl"a.sa:nent is th.e !act t.liat the Sritiah govort111""nt 

is involved concerni~1.g its moat secret sources of 1nfol"'m4tion, regs.rdin:; s~:lch 

on.ly the l'l"ime itlinister, the Chiefs of Staff and a very 11111it.O number of other 

off 1c la.ls hav• knowledge. 

"'A recent speech in Con~reu :,y ::eprosent.ative Harneu would clearly- suzgest 

to t.he Jap&u'l.eue that we have been reading their codes, thou~h ~:r. P'.arnoos and 

the Ar,erieb.n public ia-:iuld i}robs.b.13 not draw 11cy such concluaion. 

''!he concuct. of ~nnera..l 1ieenhowrer 1 a camp11dt.:n and. of all ope rat lone in t lie 

i l'lcif ic a.re close.11 related in conception and t11dn's to the information we 

seoreti, obtain t.hrou~-rh these intercepted codH. T11e; contribute ~aatly to the 

) 
.. REF ID:A488117 

C 0 F I 

Yicto27 and treaendou•lT t.o the sa•ina 1n Amerioan ll••a, l:Mtth ln th• conduc.t 

ot current operations and in look1n5 towarda the earl.r termination ot th• •ar. 

•1 u presentiog thia u.tter t.o 7ou in the hope that you will ... 7our •1 

clear to avoid the tragic re.ult.a with which •• aJ'ft now threaten9d in the present 

* polttioal ~pa1gn. 

•P !nae return this letter b7 bearer. l will hold it in rq motit aecni file 

subject to J'Otu' reference eho\lld ;you eo '8eire. 

•fa.1thtul.J.r J'Olll'S1 

(Sgd) I. C. lllRSHALL." 

~ q lf ~~..._,;;-'f" .(.;,J:t;: . .- At:> ~~.,,. .. , -l'k.~~ t-€-t,.o ,,.~~"" ~~·-··""L.' 

_tl''On Yl~:n_V · .. -!-- ~.t."""4;.~Ai.f L.tJ~,,..,~<) '~~~ ~:A ·R'-~"""' t4_ '"'\Ao T\~k.f\ ..... .ri /\.A....UD . l) 

f\ . ., _ _ ) .t' 0,.(-'..--'""-" {?.~"- f"-A. ... ;....,,.., c~J :.."o-'t :::t....f:::..~'~ ... .vt= ·.. "I might add that l""""''~ .... v ...... 4;, ;{~"~ ) \*: . r. 

the recent action of Co~ress in requiring Anny and Navy investigations for 

action before certain dates has compelled me to bring back the corps conmander, 

General Gerow, whose troops are fighting at Trier, to testify here while the 

Germans are counter-attacking his forces there. This, howev&ver, is a very minor 

matter, compared to the loss of our code information."