4-530 To Thomas E. Dewey, September 27, 1944

Publisher: The Johns Hopkins University Press
Date: September 27, 1944

Subject: World War II

To Thomas E. Dewey1

September 27, 1944 [Washington, D.C.]

Top Secret

My dear Governor,

Colonel Clarke, my messenger to you of yesterday, September 26th, has reported the result of his delivery of my letter dated September 25th. As I understand him you (a) were unwilling to commit yourself to any agreement regarding “not communicating its contents to any other person” in view of the fact that you felt you already knew certain of the things probably referred to in the letter, as suggested to you by seeing the word “cryptograph,” and (b) you could not feel that such a letter as this to a presidential candidate could have been addressed to you by an officer in my position without the knowledge of the President.

As to (a) above I am quite willing to have you read what comes hereafter with the understanding that you are bound not to communicate to any other person any portions on which you do not now have or later receive factual knowledge from some other source than myself.2 As to (b) above you have my word that neither the Secretary of War nor the President has any intimation whatsoever that such a letter has been addressed to you or that the preparation or sending of such a communication was being considered. I assure you that the only persons who saw or know of the existence of either this letter or my letter to you dated September 25th are Admiral King, seven key officers responsible for security of military communications, and my secretary who typed these letters. I am trying my best to make plain to you that this letter is being addressed to you solely 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 preferred3 to talk to you in person but I could not devise a method that would not be subject to press and radio reactions as to why the Chief of Staff of the Army would be seeking an interview with you at this particular moment. Therefore I have turned to the method of this letter, with which Admiral King concurs,4 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:5

The most vital evidence in the Pearl Harbor matter consists of our intercepts of the Japanese diplomatic communications. Over a period of years our cryptograph 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 Department providing us with the information—but which unfortunately made no reference whatever to intentions towards Hawaii until the last message before December 7th, which did not reach our hands until the following day, December 8th.6

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.

The current raids by Admiral Halsey’s carrier forces on Japanese shipping in Manila Bay and elsewhere were largely based in timing on the known movements of Japanese convoys, two of which were caught, as anticipated, in his 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 Jap, any suspicion of the vital sources of information 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 appeared 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 military attache Japanese code all over the world was changed, and though this occurred over a year ago, we have not yet been able to break the new code and 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.7

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.8

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.9

Please return this letter by bearer. I will hold it in my most secret file subject to your reference should you so desire.10

Faithfully yours,

Document Copy Text Source: George C. Marshall Papers, Pentagon Office Collection, Selected Materials, George C. Marshall Research Library, Lexington, Virginia.

Document Format: Typed letter.

1. At the upper left corner of the letter was “For Mr. Dewey’s Eyes Only” in capitals and underlined. The portion of the first version of this letter that Governor Dewey read on September 26 is document #4-526 Papers of George Catlett Marshall [4: 605]. The first two paragraphs of the letter printed here replaced the first two paragraphs of the September 25 letter. The balance of the letters is nearly the same.

2. When Clarke arrived at the governor’s mansion in Albany, New York, he discovered that Dewey was still suspicious of Marshall’s motives in sending a top secret message that would likely preclude the Republican party’s use of the Pearl Harbor attack in the campaign. Dewey was unwilling to read the letter unless he could keep a copy and unless Elliot V. Bell—New York state banks superintendent and a trusted speechwriter—was present and also permitted to read it. After some discussion with Clarke, Dewey telephoned Marshall, talked with him for several minutes, and arranged for these changes in Clarke’s orders. Nevertheless, the governor was still unconvinced of the need for such secrecy in the Pearl Harbor codes matter, asserting that it was “the worst kept secret in Washington.” (There was clearly some truth to this; see Marshall to Patch, June 29, 1943, Papers of George Catlett Marshall, #4-031 [4: 39-40].) Despite Clarke’s assurances, Dewey found it hard to believe that the United States was still reading two of the prewar Japanese codes: “why in hell haven’t they changed them, especially after what happened at Midway and the Coral Sea?” (“Statement for the Record of Participation of Brig. Gen. Carter W. Clarke, GSC in the Transmittal of Letters from Gen. George C. Marshall to Gov. Thomas E. Dewey the Latter Part of September 1944,” NA/RG 457 [Studies on Cryptology, SRH-043]. All subsequent quotes from Clarke are from this source.)

3. The September 25 version read: “I should have preferred.”

4. Marshall added to the September 25 version the phrase “with which Admiral King concurs.”

5. The September 25 letter read: “In brief, the military dilemma resulting from Congressional political battles of the presidential campaign is this.”

6. As he made clear in his testimony of December 7, 1945, Marshall was referring to the December 3, 1941, message from a Japanese agent in Honolulu to Tokyo establishing signals for reporting ships and their movements in Pearl Harbor. It was not deciphered and translated by U.S. cryptanalysts until December 11. (Pearl Harbor Attack, pt. 3, p. 1138. The December 3 document is printed in Department of Defense, The “Magic” Background of Pearl Harbor. 8 pts. [Washington: GPO, 1977], vol. 4 Appendix, A-151-A-153.)

7. This paragraph was added by Marshall for this version. Prior to Dewey’s reading the letter, Clarke told him: “Churchill considered this [ULTRA intelligence] his secret weapon and that it had really saved England. I described how Churchill felt about security, how the Navy prized it so highly and how difficult it had been to break down British resistance because of American lack of security consciousness. I quoted to him Churchill’s reported statement about protecting this source, how that in order to protect the source the British had time and again permitted convoys to be attacked rather than divert them from their course and thus blow security.”

8. Forest A. Harness was a Republican from Indiana. In his September 11, 1944, speech, he told the House of Representatives that “the Government had learned very confidentially that instructions were sent out from the Japanese Government to all Japanese emissaries in this hemisphere to destroy the codes.” (Congressional Record, 78th Cong., 2d sess., vol. 90, p. 7649.)

9. The September 25 version of this paragraph read: “I am presenting this matter to you, for your secret information, 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. I might add that the recent action of Congress in requiring Army and Navy investigations for action before certain dates has compelled me to bring back the Corps commander, General Gerow, whose troops are fighting at Trier, to testify here while the Germans are counterattacking his forces there. This, however, is a very minor matter compared to the loss of our code information.”

10. After Dewey and Bell had finished reading the letter, according to Clarke, the governor said: “Well, except for the matter of the two codes and the OSS, there is little in this letter that I did not already know.” After some further discussion with Clarke, Dewey and Bell left the room for about twenty-two minutes. Upon their return, Dewey reread several paragraphs and finally said: “Well, Colonel, I do not believe that there are any questions I want to ask you nor do I care to have any discussion about the contents of the letter.” He said that he had no message he wished to give to Marshall. Clarke returned to Washington that evening.

In his December 7, 1945, testimony, Marshall noted that “there was no further mention of Pearl Harbor, as I recall, during the campaign.” After the election in November 1944 and again after Roosevelt’s death in April 1945, Marshall endeavored to demonstrate to Dewey the value of the codebreaking activities to the Pacific campaign. (Pearl Harbor Attack, pt. 3, p. 1136.) News of the Dewey-Marshall agreement was not leaked to the press until a year later. See Marshall Memorandum for the President, September 22, 1945, Papers of George Catlett Marshall, #5-235 [5: 309-10].

Recommended Citation: ThePapers of George Catlett Marshall, ed.Larry I. Bland and Sharon Ritenour Stevens(Lexington, Va.: The George C. Marshall Foundation, 1981- ). Electronic version based on The Papers of George Catlett Marshall, vol. 4, “Aggressive and Determined Leadership,” June 1, 1943-December 31, 1944 (Baltimore and London: The Johns Hopkins University Press, 1996), pp. 607-611.

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