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The Japanese, after considerable consideration, decided that the best way to end the stalemate in China was to take advantage of the war in Europe and strike south. This would expand their Empire into Southeast Asia, targeting the all-important Southern Resource Zone (SRZ). Finally they could obtain the oil they needed. A few months later, the United States broke into the Japanese Diplomatic Code—designated Purple. The code-breaking operation that cracked Purple was code named Magic. Thus, President Roosevelt and key American officials were aware of precisely what Japan's objectives were, but not what the Japanese military was doing. Militaries do not send secret military plans and movements 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 complicated than what the Germans were using, and like the Germans, the Japanese were convinced 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. Decisions in Japan were made by the military, and the nationalist 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 are often misunderstood. Military plans were not transmitted on Purple. Decisions in Japan were made by the military, and the nationalist military officers did not entirely trust the Foreign Office, which was correctly seen as too committed to peaceful solutions. They certainly did not entrust the diplomats with military secrets.
The Americans cracked the Japanese diplomatic cyphers throughout the 1920s. This began with the Washington Naval Conference (1921). U.S. Army Signal Corps created the eighth section of military intelligence, MI-8 headed by Y.O Yardley. The U.S. Navy was also active. A copy of the Red code book was obtained through a 'black bag' operation, gaining access to the luggage of a Japanese naval attaché (1923). (These color names were not used by the Japanese. They were the colors of binders used by the American cryptologists. After 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】 The Japanese were outraged and set out to develop an encryption 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 assured of that throughout the War. William Friedman played an important 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 at the time, the Japanese had used some American telephone equipment to 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 Japanese encryption system as Purple and thus called the duplicate device the 'Purple Machine'. The system was called Purple because of the colored 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 control the decrypts and distribute them. The final agreement was an absurdity. They would alternate days for the messages to be decrypted. And distribution alternated alternatively. 【Budiansky, p. 168.】 The location of the Magic operation in Washington meant that information from the decrypts was 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 diplomatic messages. The Japanese code system was designed by a Japanese Navy captain. Thus, American officials were provided 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-important Southern Resource Zone (SRZ). A few months later, the United States broke into the Japanese Diplomatic Code—designated Purple. The code-breaking operation that cracked Purple was code named 'Magic'. Thus, President Roosevelt and key American officials were aware of precisely what Japan's objectives were, but NOT what the Japanese military was doing. Militaries do not send military plans and movements through diplomatic channels. Purple was helpful, but not the all-important naval codes -- JN-25. The code breakers were also trying to crack JN-25 but progress was still limited. The Purple, in addition to diplomatic matters, did include information on intelligence targets and activities. Again, Japanese counter-intelligence did not uncover Magic. The Germans learned that the United States was 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 revelations. The American program to decrypt Japanese codes also included work on imperial naval codes.
Magic gave American officials the ability to read Japanese diplomatic dispatches in near real time. Military plans were not transmitted on Purle. Decisions in Japan were made by the military, and the nationalist 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 are often misunderstood. Military plans were not transmitted on Purple. As a result, there was no information unearthed from Magic on Pearl Harbor.
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 cabaled 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 sympathetic unknown contacts in the State Department. 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 intentions. Umansky may have concluded that the United States must have either had a spy in the Japanese Foreign Ministry or cracked 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 next step that if the Americans could crack into Japanese transmissions, their own secure transmissions were vulnerable. (In fact, the British had been reading them for many months.) But the Germans seem to have thought that cracking a Japanese code was no real achievement. 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. It would sees likely that he could have done so.
American code breakers in Washington began intercepting a lengthy 14-part Japanese diplomatic message (late-Decmber 6). The first 13 parts were deciphered and passed on to the President and Secretary of State Hull. 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 (6 hours behind Washington time). The War Department sent an alert to Pearl, but because of disruptive atmospheric conditions, they used the commercial Western Union telegraph. 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 intelligence operations against the Japanese and the Pacific War. Actually, Magic was actually 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 successful, 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 embedded source with access to the NAZI hierarchy. Baron Hiroshi Oshima (大島 浩) was appointed the Japanese Ambassador to NAZI Germany before the War. He was a three-star Japanese Army general. As a result of the Axis alliance and Hitler's desire to cultivate the Japanese, he was given unprecedented access to German military planning and operations. (The Japanese did not reciprocate. 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, enciphered 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 allowing him to take detailed notes. All duly forwarded to Tokyo. The Japanese Embassy in Berlin reported back to Tokyo about not only Oshima's findings but also information obtained by other Japanese diplomats as well as Japanese officers enbeded in the Wehrmacht. And all of this was available to the Americans through Magic. Oshima in particular reported his findings in great detail to Tokyo. Not only did Oshima send detailed reports on German military operations and facilities, but he also met with ranking German officials, including Hitler himself. This means gaining insights to 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 imbedded in the Wehrmacht. Thus the Japanese obtained detailed information on the German war machine at every level. All of this was accessible to the Americans through Magic. It is why President Roosevelt was able 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 diplomatic 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. 【 National Security Archive】 The Japanese War Cabinet had instructed Tōgō to pursue the possibility of improving relations with the Soviet Union. Tōgō did not raise the more outlandish ideas expressed by his colleagues, such as an alliance with the Soviets against the Americans and British. But he was interested in improving relations and seeking Soviet intervention with the Americans. Satō was a seasoned diplomat, 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 attempted 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 phrases". And he advises that the Russians will not be interested.
July 18 -- Satō to Tōgō: Satō advises Tōgō that Japan has no choice but to accept basically unconditional surrender, except the preservation of the Imperial System.
July 21 -- Tōgō to Satō: With regard to unconditional surrender, we are unable to consider it under any circumstances whatsoever." And this is even if the Americans accepted the preservation of the imperial system.
One historian believes that the fault did not lie with Tōgō but with the other members of the War Cabinet who never had any serious intention of entering into discussions with the Soviets. The Emperor himself did not believe the Soviets were trustworthy, a sentiment widely shared in Japanese 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.
National Security Archive. "Japanese Peace Feelers" (George Washington University). You can explore declassified transcripts of these cables through the National Security Archive's Magic Diplomatic Summaries. ">Magic Diplomatic Summaries.
* 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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