The Japanese after considerable consideration decided that the best way to take advantage of the war in Europe was to strike south and expand their Empire into Southeast Asia targeting the all imortnt Southern Resource Zone (SRZ) (late-1939). A few months later, the United States broke into the Japanese Diplomatic Code--designated Purple. The code breaking operation that cracked urple was code named Magic. Thus President Roosevelt and key American officials were aware of precisely what Japan's objectves were, but not what the Japanese military was doing. Militaries do not send militaru plans and movemnts through diplomatic channels. Purple was helpful, but not the the all important naval codes -- JN-25. The Japanese Foreign Office began using the Alphabetical Typewriter 97 (1938). Purple was not an actual code, but an electro-mechanical coding system. It was a cipher machine, but less complicatted than what the Germans were using and like the Germans, the Japanese were convinved that the system could not be cracked. The U.S. Army Signals Intelligence Service (SIS) began to work on breaking into the system. Magic gave American officials the ability to read Japanese diplomatic dispatches in near real time. Military plans were not transmitted on Purle. Decessions in Japan were made by the military and the nationlist military officers did not entirely trust the Foireign Office and certainly did not entrust them with military secrets. Distribution of Magic was very carefully restricted. The use of Magic and the information contained in the messages is often misunderstood. Military plans were not transmitted on Purple. Decessions in Japan were made by the military and the nationlist military officers did not entirely trust the Foreign Office which was seen as too commited tp peceful sollutions. They certainly did not entrust the diplomats with military secrets.
The Americans cracked the Japanese dioplomatic cyphers throughout the 1920s. This began with the Washington Naval Conference (1921). U.S. Army Signal Corps created eighth section of military intelligence, MI-8 headed by Y.O Yardley. The U.,S. Navy was also asctive. A copy of the Red code book was obtained through in a 'black bag" operation gaining access to the luggage of a Japanese naval attache (1923). (These color nanmes were not used by the Japnese. They were the colors of binders used by the American code books. A 3 years, Agnes Driscoll was able to break the additive portion of the code. Knowledge of the Red Book code helped crack the similarly-constructed Blue Book code. When Yardley's code breaking operations were closed down, he wrote a book detailing his operations. [Yardley] Yhe Japanese were outraged and set out to develop anancriotion system that could not be cracked. The Japanese Foreign Office began using the Alphabetical Typewriter 97 (1938). Which the Americans called Purple. It was more complicated than Red, but very similar which helped in the cracking process. Purple was not an actual code, but an electro-mechanical coding system. It was a cipher machine, but less complicated than what the Germans were using. And like the Germans, the Japanese were convinced that the system could not be cracked. And they remained cindident of that thriughout the War. William Friedmanplayed an imprtant role in cracking Purple.
The U.S. Army Signals Intelligence Service (SIS) began to work on breaking into the system. Frank Rowlett directed the project. Finally Genevieve Grojan made a critical discovery. Although unknown atthe time, the Japamese had used some American telephone equipment yo build their purple machine. The Americans used some of the same equipment. The SIS team was thus able to build a duplicate of a maxhine that they had never seen (September 1940). The American code breakers referred to the Japane encryption system as Purple and thus called the duplicate device the Purple Machine. The system was called Purple because of the color binders that were used for the decrypts. The messages were sent through machines and the American cryptologists managed to build their own Purple machine to read the Japanese diplomatic messages. The information gained from Purple decryptions came to be called Magic within the U.S. government because the Foreign Office used it for only their most important messages. [Curtin] The Army and Navy fought over who would ontrol the decrypts nd destribute them. The final agreement wa an absurity. They would alternte days for the messages to be devrypted. And destribution alternated alternatively. [Budiansky, p. 168.] The location of the Magic operation in Washington meant that information from the decrypts were not sent to Pearl Harbor unless the War Department decided to send some of the intelligence obtained. The Purple machine was a successor to earlier machines used to read Japanese diplomsatic mesages. The Japanese code system was designed by a Japanese Navy captain. Thus American officials were provide an insight into Japanese plans, albeit not military operations.
The Japanese after considerable consideration decided that the best way to take advantage of the war in Europe was to strike south and expand their Empire into Southeast Asia targeting the all imortnt Southern Resource Zone (SRZ) (late-1939). A few months later, the United States broke into the Japanese Diplomatic Code--designated Purple. The code breaking operation that cracked urple was code named Magic. Thus President Roosevelt and key American officials were aware of precisely what Japan's objectves were, but not what the Japanese military was doing. Militaries do not send militaru plans and movemnts through diplomatic channels. Purple was helpful, but not the the all important naval codes -- JN-25. The code breakers were also trying to crack JN-25 but progress was still limited. The Purple decrypts in addition to diplomatic matters, however, did include information on intelligence targets and activities. Again Japanese counter-intelligence did not uncover Magic. The Germans learned that the United States were reading Japanese diplomatic messages and informed the Japanese (April 1941). Magic was one of the most closely guarded American secrets of World War II. It is unknown why the Japanese ignored the German relavations. The American program to decrypt Japanese codes also include work on naval codes.
Magic gave American officials the ability to read Japanese diplomatic dispatches in near real time. Military plans were not transmitted on Purle. Decessions in Japan were made by the military and the nationlist military officers did not entirely trust the Foireign Office and certainly did not entrust them with military secrets. Distribution of Magic was very carefully restricted. The use of Magic and the information contained in the messages is often misunderstood. Military plans were not transmitted on Purple. Decessions in Japan were made by the military and the nationlist military officers did not entirely trust the Foireign Office and certainly did not entrust them with military secrets.
Dr. Hans Thomsen was the Chargé d'Affaires at the German Embassy in Washington, D.C.. President Roosevelt after Kristallnachr recalled the U.S. ambassador in Berlin (November 1938). The German Government then recalled Ambassador Hans-Heinrich Dieckhoff. Thomsen
appears to have accurately assessed the Roosevelt Administration and its anti-NAZI orientation. Like Ambassador Dieckhoff, he reported to Berlin on the President's hostility. While he was in charge of the Embassy, the Isolationist Movement in America gained strength. He did what he could to support the Isolationists. They were the Americans opposing involvement in another world war. [Thomsett, p. 151.] Thomsen was involved in another even more serious incident. He cabeled the Foreign Ministry that the American Government had broken the Japanese diplomatic (Purple) code (April 1941). Thomsen's source may have been Soviet Ambassador Konstantin Umansky. It is not known how Umansky learned about Magic. It could have been unknown contacts in the State Depoaertmnent. He could have deduced it as a result of conversations with Undersecretary of State Summer Wells. Wells had access to Purple decrypts. And conversations with Umansky about Japanese intentions are believed to have occurred. As a result of Magic, the United States knew a great deal about Japanese interntuions. Umansky may have concluded that the United States must have either had a spy in the Japanese Foreign Ministry or crracked Purple. Cracking Purple apparently seemed the most plausible explanation. Unmasking the American Magic operation of course would have been a major intelligence coup. The Foreign Ministry forwarded this alert to their Axis ally. The Japanese Foreign Ministry, however, dismissed the report, believing that their codes were unbreakable. (The Germans for their part do not seem to have taken the logical step that if the Americans could crack into Japanese transmissions that their own secure transmissions were vulnerable. In fact the British had been reading them for many months.) Thomsen spent several months with Japanese diplomats at the Greenbriar resort awaiting repatriation (1942). We do not know if he raised the subject of American code breaking with them.
American code breakers in Washington late-Decmber 6 began intercepting a 14-part Japanese diplomatic message. The first 13 parts were dechipherd and passed on to the Preident and Secretary of State. The final part of the Japanese message informed the Embassy that diplomatic relations with the U.S. were to be broken off were not decoded until early December 7. This was a virtual declaration of war. The 14th part was decoded about 9:00 AM. Code breakers intercepted another Japanese message about 10:00 AM. The second message instructs the Embassy to deliver the main message in the first 13 parts to the State Department at 1:00 PM. American officials noted that this time is the morning at Pearl Harbor is 6 hours behind Washigton time. The War Department sent an alert to Pearl, but inadvertedly used a commercial telegraph because radio contact was temporarily cut. The message did not arrive at Pacific Fleet headquarters on Oahu until 12:00 noon (Hawaii time) fully 4 hours after the Japanese attack had begun.
Magic is generally associated with intelligece operations against the Japanese and the Pacific War. Actually, Magic was a major source of intelligence on the Germans and the war in Europe. The Allies were unable to place and maintain intelligence agents in Germany. Some reports came out of the Reich, but they were from anti-NAZI Germans. The Soviets were more succesful, especially before Hitler invaded the Soviet Union and closed down the Soviet Embassy. The Soviets also ran some effective spy rings. The United States did have one very effective source -- an enedded source with access to the NAZI hierarchy. Baron Hiroshi Oshima (大島 浩) was appointed the Japanese Ambassador to NAZI Germany before the cWar. He was three-star Japanese Army general. As a result of the Axis alliance anf Hitler's desire to cultivate the Japanese, he was given unprecedented access to German military planning and operations. He not only developed close relations with the NAZI hierarchy, but also the Wehrmacht. Here he is inspecting Germany's Atlantic Wall defenses during November 1943 (figure 1)). His 20-page report enchiphered in Purple was transmitted to Tokyo and intercepted and read by the Americans. It was like giving a spy a tour of the beach defenses and allping him to take detrailed notes (figure 1). All duly fowarded to Tokyo. The Japanese Embassy in Berlin reported back to Tokyo about not only Oshima's findings but other Japanese diplomats as well as Japanese officers enbeded in the Wehrmacht in great detail. And all of this was available to the Americans through Magic. And he reported his findings in great detail to Tokyo. Not only did Oshima send fetailed reports on German military operatioins andfacilities, but hevmet with ranking German officils, imcludingHitler himslf, and their assessments at different points in the War. And it should not be thought that Oshima did all of this alone. There were Japanese embassies located throughout NAZI occupied Europe as well as Rome and neutral countries. And there was a Japanese military mission in Rome which included Japanese officers inbeded in the Wehrmacht. Thus the Japanese had detailed information on the German war machine at every level. All of this was accessable to the Americans through Magic. It is why President Roosevelt was able to to personally warn Stalin about Barbarossa. After the War, none other than General George C. Marshall, identified Ōshima as 'our main basis of information regarding Hitler's intentions in Europe'.
Magic did not stop with the NAZI surrender. Purple decryots enabled the Americans to follow Japanese dipolmatic traffic. Some of the most useful traffic was a series of messages between Foreign Minister Shigenori Tōgō in Tokyo and Ambassador Naotake Satō in Moscow. The Japanese War Cabinet had instructed Tōgō to persue the possibity of imoroving relatiions with the Soviet Union. Tōgō did not raise the more outlandish ideas expressed by his colleages such as an alliance with the Soviets against the Americans and Britush. But he was interested in improving relatuions and seeking Soviet intervention with the Ameticans. Satō was a seasoned dipolomat, a former foreign minister and understood the Soviets fairly well. In fact he had tried to see Molotov who ignored his requests. Satō was frustrated by Tōgō's absurd messages and attemoted to convey a badly needed sense of reality. Tōgō's messages were wordy and vague, probably because he did not want to admit just how dire the situation was:
July ? -- Satō to Tōgō: A frustrated Satō curtly tells Tōgō, " ... the reasoning in your message of 11 Juky consists of nothing more than academic fine phraases." And he advises that the cRussians will not be interested.
July 18 -- Satō to Tōgō: Satō advises Tōgō that Japan has no choice but to aaceot basically unconditional surrender, exept the preservation of the Imperial System.
July 21 -- Tōgō to Satō: With regards to unconditionl surrender m we are unable to consider it under any circustances whatever." And this is even if the Anericans acceoted the oreservation of the impperial system.
One hisdtorian believes that the fault did lie with Tōgō but the otrer menbrers of the War Cabinent wjonnever had any serious intention of entering into discussions with the Soviets. The Emperpr himself did not believe the Soviets were trustworthy, a sentiment weidek shared in Loanese Government circles. [Barrett]
Barrett, David Dean. 140 Days to Hirishima.
Budiansky, Stephen. Battle of Wits: The Complete Story of Codebreaking in World war II (Simon and Schuster--Touchstone: New York, 2002), 436p.
Curtin, Matt. Brute Force.
Drea, Edward J. MacArthur’s ULTRA: Codebreaking and the War against Japan, 1942-1945 (University Press of Kansas: Lawrence, Kansas, 1992).
Dreaa, Edward J. and Joseph E. Richard. "New evidence on breaking the Japanese army codes," Intelligence and National Security Special Issue: Allied and Axis Signals Intelligence in World War II. Vol. 14, Issue 1 (1999), pp. 62-83.
Lewin, Ronald. The American Magic Codes, Cyphers and the Defeat of Japan.
* Thomsett, Michael C. The German Opposition to Hitler: The Resistance, the Underground, and Assassination Plots, 1938-1945 (McFarland & Company: 1997).
Yardley, Herbert O. The American Black Chamber (1931).
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