Let us agree that the question raised is not a foolish one, but let us consider it in two parts. First, as to why the British got the system. In the autumn of 1940 U.S. military and naval authorities on the highest level agreed that there should and could be some exchange of intelligence between the U.S. and the U.K. Included in the material to be exchanged was communication intelligence. It was ascertained that the U.K. communication intelligence experts had not succeeded in solving the highest-level Japanese diplomatic cryptosystem and the machine which was involved in enciphering and deciphering the messages in that system.. (Nor, parenthetically, had the German experts.) Cryptanalysts of the U.S. Army's Signal Intelligence Service, however, had accomplished this task and were reading the Japanese messages in that cryptosystem, which
they had named, for brevity as well as for disguise, the PURPLE system, its predecessor, also a machine system, having been named the [censored] system. On the other hand, it had been ascertained that the U.K. cryptanalysts, although they had been unsuccessful with the PURPLE system, had been quite successful with certain German diplomatic cryptosystems, the study of which had only recently been undertaken by U.S. cryptanalysts. It therefore seemed that both the U.S. and U.K. could profit by some sort of exchange. A team of four cryptanalysts, two from the Army and two from the Navy, was sent to London in January of 1941 to discuss the technical aspects of an exchange of material. The U.S. team took with it a recently-completed PURPLE machine and the data necessary to use it in deciphering the Japanese messages. It is very important to understand that the British had not only extensive facilitates for intercepting and forwarding Japanese diplomatic traffic to London, but they also had a corps of very competent cryptanalysts and Japanese translators--without whom possession of the PURPLE machine would have been of little or no value. The British also were able to read and translate other systems carrying Japanese diplomatic traffic--and they did so not only in London but also at Singapore and Hong Kong, and possibly in one or two other strategic spots under the British Crown.
In the exchange of the PURPLE machine and informational details concerning the PURPLE system for specific technical data on certain German cryptosystems (principally diplomatic), both the U.S. and the U.K. gained advantages of inestimable value. On this point there never has been any doubt on either side. Moreover, this exchange paved the way
to a later complete U.S.-U.K. collaboration in cryptanalytic operations after the U.S. entry into World War II as one of the belligerents. The value of this collaboration can hardly be overestimated, but this brochure will not deal with this aspect.
As long as we are dealing with the question about the U.S. delivery to the British of a PURPLE machine and the cryptosystem which used it, we may well go into a related question concerning which little has been said in the torrent of words about the Pearl Harbor disaster. The British acquired the PURPLE in January 1941, and were able from the very first to use it--no strings were attached to this usage, except that the secret would be treated with the care that it deserved in order to keep from enemy knowledge the fact that we had solved it. (There have always been very detailed and strict regulations governing the handling of communications intelligence and in time the U.S. and U.K. regulations became identical). The reason for mentioning that there were no strings attached to the U.S. gift to the British is to forestall a revisionist allegation that President Roosevelt must have permitted the gift to be made only on condition that no information coming from PURPLE would be used by the British in a manner that would interfere with his conspiracy to withhold from the two commanders at Pearl Harbor whatever intelligence they might obtain which would prevent the Japanese taking them by surprise. Such an allegation would, of course, be absurd on its face--but then the revisionists do not always argue in a logical manner. Exactly whey the Births would, even if they could have agreed, to keep PURPLE intelligence from Short and Kimmel is hard to understand. In the first place, although there
was no direct communication between these commanders and the British, certainly, there was communication between British and American intelligence authorities in the Far East. In the second place, let it be noted that the British had been able to read and were reading Japanese diplomatic systems other than PURPLE; in fact, many of the messages which the revisionists claim most definitely indicated that a surprise air attack was to be made at Pearl Harbor were in cryptosystems other than PURPLE. For example, the so-called "bombing plot" message was not in PURPLE at all but in a system held by consulates, a system designated by us as [censored]; and several other messages related to the bombing plot message were in the same systems.
What has all the foregoing to do with the British? Simply this: is it conceivable that the Births, too, would have participated in a conspiracy of silence so as to let the Japanese destroy the U.S. Pacific Fleet, the fleet that was their principle protection against Japanese aggression in the Far East? Hardly. Is it not clear that the various messages in PURPLE and in other Japanese systems conveyed to the British no definite statement as to an impending attack on the American bastion in the Hawaiian area? The Births, let us remember, were then supposed to have the finest and most carefully trained intelligence experts in the world. Is it likely that the detailed story of an impending attack, if revealed by MAGIC, would have been completely overlooked by their experts? Is it conceivable that they would, if they saw the outlines of the story, have kept it to themselves? That they would have kept it from their U.S. friends? That they would have seen to it that no word of it
leaked to Short and Kimmel? The British were counting upon the U.S. to protect British interests in the Far East.
In the foregoing paragraphs it was stated that certain Japanese messages were long-delayed in their processing into plain English by the Army and Navy cryptanalytic units. These delays were caused by several things: (1) there were so many messages to b e forwarded from U.S. intercept stations that U.S. radio facilities were then not equal to the task of carrying them all; many had to be sent by air mail pouch or even by ordinary U.S. Mail pouch; (2) there were so many messages and so few person capable of processing them in Washington--let us not forget that a few dozens of persons in Washington were trying to keep up with what hundreds, perhaps thousands, of Japanese were doing in Japanese message centers in Japanese embassies, legations, and consulates all over the world; (3) there were many times when it was impossible to solve a new key until a sufficient amount of traffic had accumulated: 94) there were many cases when decrypting a message was stymied by errors in transmission or interception; (5) there were only a handful of persons in both the Army and the Navy cryptanalytic units who could translate Japanese--and no pool in the U.S. from which trained and trustworthy Japanese translators could be selected, as is the case in other foreign languages such as French, German, Spanish, etc.; and until the Japanese was converted into English, the messages containing useful intelligence about Japan might just as well be filed in the waste basket.
While we dwell upon the foregoing elements in the story it might be a good place to point out that a conspiracy to withhold information in
order than an attack might be carried out could hardly afford to risk certain contingencies. For instance, it would be essential, would it not, that a high degree of priority in processing be accorded all Japanese Government messages going to or coming from Honolulu, so that the alleged conspirators themselves might not be caught napping? But it is a fact that several very important messages having a direct bearing on the situation were not processed until several days after the attack. The very fact that the processing of al messages to and from Honolulu was not given the highest or even a high priority itself constitutes an argument against the alleged conspiracy being objective--and not completely subjective.
Republican, who had learned about MAGIC (nobody knows how or from whom). Marshall had learned that Dewey was proposing to use this highly explosive information in the 1944 Republican Presidential campaign against a fourth term for Roosevelt. The war was not over! Here it is, in extenso:
Extracted from CONGRESSIONAL INVESTIGATION PEARL HARBOR ATTACK,
Part 3, pp. 1132-1133.
For Mr. Dewey's eyes only. 27 September 1944.
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 how have or later receive factual knowledge from some other source than myself. 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 interest 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 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, 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 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 Sate (2987E] Department providing us with the information--but which unfortunately made no 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.
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.
The Roberts' report on Pearl Harbor had to have withdrawn from it all references 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.
[2987F] 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.
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.
(Sgd) G.. MARSHALL.
It seems to me that the foregoing letter goes a long way toward answering the question as to why MAGIC was withheld from Kimmel and Short. Stated briefly, the authorities in Washington were fearful that if MAGIC continued to be sent them the secret that we were able to read all their diplomatic cryptocommunications, including PURPLE, their most secure system, would soon find its way to the Japanese. The whole of the island of Oahu had thousands of Japanese nationals, among whom it was natural to assume there were--there must have been--plenty of spies. The Army and Navy authorities in Washington felt that it was becoming too dangerous to the continued secrecy of the fact that we had solved and were reading messages in PURPLE to send any more of the messages to Kimmel and Short. Of course, they could have been sent some gists--as had been done in the first half of 1941--but General Sherman Miles, the then Assistant Chief of Staff for Military Intelligence, stated before the Joint Congressional Committee that sending even gists would have been dangerous, by overloading the radio circuits; and he went on to say that while the Navy cryptosystems could have been used, because they were more secure than the Army's, even that would not remove the danger altogether. (I will interject at this point the statement that General Miles was not too well-informed on these practical matters, because the navy had adopted and was using an Army cryptosystem and a machine invented by Army personnel!) Both the Army and the Navy's cryptosystems could and would have stood up under the strain of sending all the important MAGIC messages to Kimmel and Short and in extenso.
But, insist the revisionists, the Navy furnished a MAGIC machine and information on how to use it to the Commander of the 16th Naval District--the Philippines. Why not to Kimmel and Short? There were very good reasons for this; but at this point we shall merely ask: did possession of MAGIC prevent General MacArthur from being taken by surprise and losing all his planes at one fell swoop more than 12 hours after the General knew of the Japanese attack on Pearl Harbor? General MacArthur blames hi chief of the Army Air Corps forces in the Philippines, General Brereton, for being caught napping; and Brereton blames MacArthur. Possession of the PURPLE machine alone obviously was not sufficient--the interpretation, appreciation, and evaluation of MAGIC is just as important. It might be useful to quote what General Willoughby, MacArthur's G-2, said on this latter point in an affidavit dated 8 May 1945 (PHR, Part 35, p. 87) in protecting the Navy's monopoly of MAGIC:
In 1941 the Navy obtained and maintained a highly efficient crypto-analytical service, specializing in Japanese material; though the Army had notably participated in the development of this subject, the Navy appears to have obtained a lead; consequently, it can be said that the Navy enjoyed an almost monopolistic privilege. In an otherwise meritorious desire to security (though every modern nation knows that crypto-analysis is going on, the Navy has shrouded the whole enterprise in mystery, excluding other services, and rigidly centralizing the whole enterprise. At this date, for example, this same system is still in vogue: as far as SWPA is concerned, the crypto-analysis is made in Melbourne, forwarded via 7th Fleet D.N.I.; the Melbourne station is under direct orders of Washington, is not bound by any local responsibilities, forwards what they select, and when it suits them .The possibility of erroneous or incomplete selection is as evident now as it was in 1941. The only excuse the Navy has is that its field is primarily naval intercepts, but there is a lot of Army traffic or other incidental traffic. This collateral traffic is not always understood or correctly interpreted by the Navy, in my opinion.
The solution to this vexing and dangerous problem is a completely joint, inter-locking intercept and crypto-analytical service, on the highest level, with the freest interchange of messages and interpretation.
The sequence of messages referred to, had they been known to a competent intelligence officer, with Battle Order and tactical background, beginning with November 14th, would have led instantly to the inescapable conclusion that Pearl Harbor naval installations were a target for attack ,with November 25th or November 29th as the deadlines, suggesting irresistibly that elapsed time was involved, for some sort of naval seaborne sortie.
Major General, G.S.C.,
Asst. Chief of Staff, G-2,
General Headquarters, SWPA.
The fact is that skilled cryptanalytic help and skilled Japanese translators were not in sufficient supply to permit either the Army or the Navy to maintain many such people anywhere outside the U.S.--they were badly needed in Washington. And besides, nobody thought or even imagined that they were so badly needed at Pearl Harbor as at Manila--the Japanese would never be so foolhardy as to attack Pearl! The U.S. Navy authorities believed that the Philippines might be cut off--but not Hawaii. Manila needed MAGIC much more than Pearl! That explains why there was a PURPLE machine in Manila, more than anything else. The Navy communications personnel at Pearl were assigned the mission of trying desperately to solve the important Japanese naval cryptosystems and to get what information could be gleaned from traffic analysis of Japanese communications; the Army had no signal intelligence or cryptanalytic personnel at all in Hawaii after 1939--the very small unit it did have in Honolulu was brought back to Washington after but one year's operations there--because the few trained persons of that unit were thought
to be much more useful in Washington. Hawaii seemed to be the last place the Japanese would try to attack! Why keep the few trained cryptanalytic personnel there when they could be so much more useful in Washington? What the Army had, therefore, was simply an intercept unit directed to listen in on certain assigned Japanese circuits and to forward the traffic to Washington for study.
In this decision to bring back to Washington that small Army cryptanalytic unit (two or three persons at most!) I am quite sure that the Chief Signal Officer consulted no higher authority--and, I am sure too, the Commanding General of the Hawaiian Department at that time, General Short's predecessor, was glad to get rid of the unit--its maintenance caused him difficult logistical problems. The secrecy of its operations certainly was a source of irritation to him and his staff--they never got to see the results. The trained Signal Corps officer the Signal Intelligence Service in Washington sent to Hawaii in 1940 performed no signal intelligence functions; by direction of the local commander he was soon given "more necessary" duties, such as devising and supervising the laying of communication cables in and around Honolulu. And with this decision I can take no exception--the Commanding General on the spot knew best what he needed. I know for a fact that when the Signal Corps sent a very small unit to Corregidor it was only with the greatest difficulty that the Commanding General there was finally persuaded to let the unit do what it was sent out to do--but only for a short time. The members of any Signal Intelligence unit (Signal Corps personnel) were badly needed for ordinary Signal Corps functions. Washington could do
very little about this--the local commander decided. In all that I have said above, however, the most important point by far was, so far as concerned both the Philippines and Hawaii, that an attack by the Japanese was too fantastic to warrant much thought, so preparations for a possible attack were somewhat neglected.