** World War II -- country code breaking America United States

World War II: Country Code Breaking Efforts--The United States

Figure 1.--The Pacific Ocean is huge, the distances daunting. The basic problem for naval commanders in the Pcific was finding enemy naval forces in this vast watery expanse. Doing so and launching the first strike was key in carrier battles. Inexplicably at the critical point in the Pacific War, the out-gunned and out-manned American carriers turned up at just the right time and place to intercept the Japanese Carriers, not once, but twice. First in the Coral Sea (May 1942) and then at Midway (June 1942). The odds that this was accidental defy credulity. Despite the obvious inference (cracked naval codes), Japanese Naval commanders like their German colleagues remained convinced throughout the War that their naval codes were secure. The Japanese were even inforned by German sources that their codes had been cracked. The planes here are the same Douglas Scout Boomber Dauntless (SBD) dive bombers which operating with information from cracked JN-25 messages devestated four front line Imperial Navy carriers at Midway. This literaly tore the heart out of the Imperial Japanese Navy, a loss from which it never recovered. We are not sure precisely when this photograph was taken, but it was apparently taken in 1943. Nor do we know from which carrier this squadron was launched. The SBD proved a very effective dive bomber, but required fighter escorts. The suceeded at Midway without fighter cover because the Japanese Zeros protecting the carriers came down to the surface to engage the American torpedo squadeons which found the Japanese first.

Historians both during and after the War did not know just why American carriers showed up at just the right time and place in the Coral Sea or at Midway. Neither did the Japanese. The answer of course was Magic. This was the code name for the top-secret code breaking operation which alerted the Americans to the Japanese plans. The same American code breaking operation that had learned of the Port Moresby operation, also warned Admiral Nimitz that the next target was Midway. American code breakers broke into the Japanese Foreign Office's top secret system for sending messages (September 1940). The American cryptologists named it Purple. The information gained from Purple decryption came to be called Magic within the U.S. government because the Foreign Office used it for only their most important messages. 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 diplomatic messages. The Navy at Pearl Harbor had its own code breaking operation working on the Japanese naval code--JN-25. Station HYPO at Pearl finally cracked JN-25, leading to the Battle of the Coral Sea and Midway. Midway was the most decisive naval battle of the War. After Pearl Harbor, American code breakers in cooperation with the British began to focus on German communications.

World War I

The United States had not participated in a major war since the Civil War (1861-65). As a result, Americans had little expertise with cryptology when Congress declared war (April 1917). Parker Hitt, a Signal Corps instructor, published a short book on cryptology (1915). He went with the American Expeditionary Force (AEF) to France as a staff officer, but commanders there sought him out for advice on cryptographic issues. A young Signal Corps officer. Joseph Mauborgne, also emerged in cryptographic work. The first AEF Doughboys arriving in France during 1917 were largely untrained. As a result, the AEF did not move up to the front for nearly a year. While training in France, the AEF on its own began developing code books. The AEF was not committed until the German Spring offensive threatened to break through Allied lines (May 1918). The AEF also began adopting French codes. A Captain Howard R. Barnes became especially adroit at turning out these codes. The Americans named their first codes after rivers, beginning with 'Potomac'. The Americans printed the code books on paper that burned easily and degraded after a few weeks by which time the codes would presumably be changed. A font was chosen for readability under trench conditions. American code makers found that combat units under the pressure of action were unable or unwilling to use the codes. Back in Washington, the War Department began working on cryptology. One of the great figures in American cryptology is Herbert O. Yardley, a brilliant, but flawed figure. He was the director of Military Intelligence's crypto-analytic service MI-8 during World War I. Their primary objective was to break German codes.

Post-War Effort: The Black Chamber

Most of the U.S. Army after World War I was stood down. Yardley's operation was, however, continued. He set up shop in New York where he operated his code-breaking operation under a commercial cover. It was the famed "American Black Chamber". Rather than the Army, it was funded by both the Departments of State and Navy. After the War, America's most pressing foreign policy problem was Japan and the growth of Japanese naval power. The Harding Administration convened the Washington Naval Arms Limitation Conference (1921-22). The Black Chamber succeeded in breaking the Japanese diplomatic code. American diplomats used the decripts at the Conference. This was unknown to the Japanese.

Closing the Black Chamber

Republican President Hoover appointed Henry Stimson Secretary of State (1929). In a great irony of history, Stimson closed down the Black Chamber with the dismissive comment, "Gentlemen don't read other gentleman's mail." Democratic President Roosevelt would later bring Stimson into his cabinet as Secretary of War to create a bipartisan consensus on war issues (1940). As Secretary of War, Stimson had lost his scruples about reading Japanese signals. It would be Secretary Stimson that oversaw the Magic decrypts of Japanese diplomatic messages that revealed the Japanese aggressive march toward war in the months before the Pearl Harbor attack.

Army Signals Intelligence Service/Navy Code and Signal Section

While Secretary Stimson ended State Department funding and effectively closed down Yardley's Black Chamber, he did not stop American code breaking which is why as Secretary of War a decade later he was reading decoded Japanese diplomatic messages and no longer complaining about gentlemanly behavior. The US Army took over the Black Chamber files and established its own code-breaking group, the Signals Intelligence Service directed by William Friedman. The U.S. Navy had previously established a Code and Signal Section within the Office of Naval Intelligence (1924). Both services focused initially on breaking Japanese codes. The problem was that virtually no one in America knew anything about developing codes, let alone breaking foreign codes.

U.S. Army efforts

The United States upon entering World War I made small expenditures for cryptology. This was done through the U.S. Army and State Department. The effort was overseen by Y.O. Yardley and became known as the Black Chamber. Yardley's highly effective operation was shut (1929), which is one reason he went public with his tell-all book, alerting the Japanese to the fact that their codes had been broken. The Army subsequently had second thoughts. [Yardley] A new code breaking effort was set up -- the Signal Intelligence Service (SIS), a unit of U.S. Army Signal Corps. Outside of the Chief Signal officer, however, virtually no one knew it existed. SIS was in effect the predecessor to the modern National Security Agency (NSA). The task was entrusted to William Friedman who hired three 'junior cryptanalysts' (April 1930). He chose Solomon Kullback, Frank Rowlett, and Abraham Sinkov. They were mathematicians with no crypto analytical experience. Friedman himself was a geneticist who developed his expertise in cryptology at George Fabyan's Riverbank Laboratories Cipher Department (1915-17) before America entered World War I. In addition to code breaking, they were given responsibility for the War Department's code systems. The SIS initially worked on an extremely limited budget, lacking the equipment it needed to even intercept messages to practice decrypting. This was increased slightly as the Japanese moved toward war in the Pacific. The American focus was on Japanese codes. With these limited resources Friedman managed to crack the Japanese diplomatic (Purple) code about a year before Pearl Harbor. The decrypts became known as Magic. Pearl Harbor of course changed everything. Suddenly vast resources were channeled into code breaking. And the American code breakers began working on German codes. Here they were vastly aided by the accomplishments already made by the British at Bletchly Park. The massive World War II SIS code breaking effort was conducted at Arlington Hall. SIS took possession of the facility under the War Powers Act (June 10, 1942). Arlington Hall, a former girls' school) became the counterpart to Britain's Bletchley Park. (The major difference was that Bletchley also worked in naval codes.) Arlington Hall concentrated its efforts on the Japanese systems, at first primarily Purrple/Magic and Bletchley concentrated on European combatants, of course primary the Germans. The focus on the Japanese diplomatic codes meant that Japanese army codes were not solved for some time (April 1943). A new organizatiin was developed (September 1943). The Japanese Army code effort was overseen by Solomon Kullback -- B-II. The diplomatic work was overseen by Frank Rowlett which also had the Bombes (primitive computes) and Rapid Analytical Machinery. The third branch translated the decrypts (B-I). It should not be thought that Magic only produced information on the Japanese. Baron Ōshima in Berlin was very close to important NAZIs, including Hitler, who shared information with him. He sent lengthy reports to Tokyo providing American code breakers a wealth of information about the German war effort. After the War, General Marshall identified Ōshima as "our main basis of information regarding Hitler's intentions in Europe". [Boyd] In the middle of the War, SIS began intercepting Soviet traffic sent mainly from New York City (1943). Much of this was sent by the Soviet Lend Lease unit. SIS named the effort to crack the Soviet code the Venona Project. By the end of the War (1945), SIS had transcribed some 0.2 million messages showing massive Soviet activity. Much of this was legitimate Lend Lease traffic, but the suspicion was that there was also messages concerning the Soviet spy networks in America. Meredith Gardner made the first break into the Venona code (December 20, 1946). As the Venona messages began to be decrypted, American officials began to unravel the extent of Soviet espionage and the fact that they had penetrated the Los Alamos National Laboratory work on the top-secret Manhattan Project.

U.S. Navy efforts

The U.S. Navy during World War I in contrast to the Army did not get substantially involved in code breaking. and America was only in the War for about 1 1/2 years. One outcome of the War was, however, a $100,000 slush fund. This was a lot more in 1910s dollars than modern dollars. The money was controlled by the Director of Naval Intelligence and kept secret from Congress. Little of this money was spent during the War. After the War, a small amount was used to fund break-ins at the Japanese Consulate in New York City. This netted the Navy the Japanese Navy's 'Red' code book. [Budiansky, p.5.] The Navy hired linguists to translate it. Meanwhile Yardley and the Black Chamber were working on the Japanese diplomatic codes. After the War, the Navy had a code unit consisting of one man--Lieutenant Laurance F. Stafford. Stafford knew nothing about codes, let alone code breaking. He received orders to devise new naval codes (1924). Knowing nothing about codes, he decided on his own that a good beginning point would be to have a lose look at foreign codes. Thus the 'research desk' in the Old Navy Department Building was born. It would develop into one of the most important parts of the U.S. Navy's World War II effort. Soon after, Joseph J. Rochefort, showed up for duty to assist in the effort. (He and other Navy cryptologists would later play a central role in the Battle of Midway.) Like Stafford, he knew nothing about codes and selected because he was known to like newspaper crossword puzzles (1925). Together they would work out the additive system, but the Japanese complicated their wotk by updating the Red Code and additives. And Yardley after Secretary Stimson discovered decoded messages was quickly out on the street without a job and broke. He then not only sold code breaking details to the Japanese, but then published a book on it (1931). [Yardley] The outraged Japanese, in part because Yardley published the account that he had secretly sold to them, proceeded to update their code systems by adopting cipher machines. This of course greatly increased the monumental challenge faced by the Navy code breakers. Simmering tensions in the Pacific caused the Navy to devote increasing resources on code breaking. Stafford's one-man research desk operation gradually grew into OP-20-G. This was the Navy's centralized code breaking operation in Washington. Their focus was on AN, the cipher reincarnation of the Imperial Navy's Red code. It would later become known as JN-25. The Navy set up interception facilities in Hawaii, Guam, and the Philippines (Cavite). The British were also hard at work at Singapore and Australia. Some progress was made, but not enough to read the messages. And as the Army had cracked the Japanese diplomatic Purple code (Magic), some Navy personnel were used to work on Purple messages, reducing the effort on JN-25. When the Japanese launched the Pacific War by attacking Pearl Harbor. By chance Rochefort commanding the Navy code unit at Pearl which would become known as Station Hypo.

Bell Labs

Bell Labs was a research unit operated by a partnership between the American telephone giant--American Telephone and Telegraph and Western Electric. They did a great deal of top secret work during the War, perhaps its greatest success was perfecting the British cavity magnetron technology and creating a prodyct which could be mass produced. The British wartime code breaker Alan Turing visited the labs at this time. Bell Labs invented or improved numerous military systems, including two-way radio, proximity fuses, semiconductor devices, radar, sonar, computers, the 'bazooka', and the first encrypted communications systems -- SIGALY (1943). Until this, the Germans had been listening to the telephone conversations between President Roosevelt and British Prime-Minister. SIGSALY was the first digital scrambled speech transmission system (1943). A reader tells us, "There is an interesting side note to your story. My godfather, Amos Joel, was part of the Bell Labs team assisting Alan Turing. Bell Labs broke the higher level German codes. While that was going on, the U.S. military wondered whether the Germans or the Japanese could break our codes given that we had broken theirs. To that end, the military commissioned a mini-Manhattan project to develop the first truly unbreakable code. When the team thought they had succeeded, they asked Amos Joel to attempt to crack their new code. He required 2 1/2 to do so on his first attempt and just 15 minutes by his fourth attempt. Thereafter he was essentially translating. After the war, Amos was awarded dozens of patents, including one for the first prime-number, public key encryption system. In 1971 he applied, as the sole named inventor, for the patent that made mobile telephony possible. His one invention taught how a virtually limitless number of people could use a very limited number of frequencies to communicate simultaneously and further taught how they could do so while traveling. Remarkably, Amos was awarded the Kyoto Prize, Japan’s highest private award for global achievement given to those who have contributed to humanity with their work." [Quinto]

Japanese Codes

The Japanese had no idea that their codes after World War I had been broken. The secret was never uncovered by the Japanese counter-intelligence services. Rather the Americans announced what they had done. The unemployed Yardley published The American Black Chamber. As a result, the Japanese changed their entire code and cipher system, closing off access to the Americans for several years. The Japanese developed a cipher machine similar to the German Enigma Machine which the Foreign Ministry used. The American code breakers referred to as Red. Subsequently they introduced a more advanced machine which the Americans called called Purple (1937). The Japanese Foreign Ministry considered it unbreakable and used it for their most sensitive communications. The Americans cracked Purple more than a year before Pearl Harbor, but not the all-important JN-25 naval codes. This break through only came after Pear Harbor. Other codes including the Maru codes and the Imperial Army codes were also cracked. Despite obvious coincidences just as the American carriers turning up at just the right time and place, the Japanese never believed that their signals were compromised. They even ignored a German report that the codes had been cracked. The information obtained by the code breakers played a vital role in the Pacific War. Japanese analysts were convinced that their improved code systems and the complexities of the Japanese language would make their codes impenetrable. Many Japanese security specialists were convinced that the Japanese language itself was a protection against Allied code breakers. And even amazing American actions like Miday and the Yamamoto shoot down did not cause the Japanese to doubt the security of their codes.

American-British Cooperation (1940)

Code cracking is among a nation's most guarded secrets. America and Britain began to cooperate as Europe moved toward war, but the first contacts were limited, in large measure because Prime-Minister Chamberlain was convinced that he had the ability to percent a war and did not want the Americans muddying up the waters. He did not desire to share British secrets with the Americans, he only wanted access to American weapons and supplies. This changed rapidly after Winston Churchill became prime-minister which occurred just as the Germans launched their western offensive (May 1940). Churchill did not have a lot to offer the Americans at the time and Britain was increasingly desperate to obtain American aid with the fall of France. The one asset Churchill did have was British research on advanced weaponry such as radar. Very quickly after these exchanges began, the British learned of the American code breaking efforts in the Pacific. And soon the two countries were working together on Japanese, German, and other country codes. The British effort was based at Bletchely Park. The Americans work was centered in Arlington Hall. The initial American effort was on the Japanese codes, but soon the Americans also mounted a major effort on German codes as well. Eventually the American code breaking effort would be much larger than the British effort. The Americans made the break through on the Japanese codes. The British sharing of Ultra gave the American work on German codes a boost that could have taken several years to have developed on their own. And the American contribution substantially increased the number of German messages that could be processed.

Japanese Diplomatic Code

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) (late-1939). 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 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 Purple. Decisions in Japan were made by the military and the nationalist military officers did not entirely trust the Foreign 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. Decisions in Japan were made by the military and the nationalist military officers did not entirely trust the Foreign Office which was seen as too committed to peaceful solutions. They certainly did not entrust the diplomats with military secrets.

Cracking the JN-25 Naval Codes (March-May 1942)

Much more important was the Japanese Navy's code which American cryptologists called JN-25. (JN for Japanese Navy and 25 for the 25th code they worked on.) The Purple diplomatic code was of great value. JN-25 was the mother lode. The Imperial Navy JN-25 proved much more difficult. Most of the American work on JN-25 was conducted by the Navy at Pearl Harbor--Station HYPO. It was an enciphered code, producing five numeral groups which was what was actually broadcasted. It proved more difficult to break than Purple. It was not until months after Pearl Harbor that the cryptologists at Pearl (Station Hypo) and the British in Ceylon began breaking into JN-25. While it was only partially cracked. JN-25 decrypts played a major role in the Battle of the Coral Sea (May 1942). For the most part intercepts could be only partially read, but enough to make some sense of Japanese intentions. American and British and American code-breakers intercepted Japanese Navy signals which revealed a planned operation toward Australia (March 1942). Code-breakers at Station Hypo led Commander Joe Rochefort produced a decrypt that revealed a naval force from Rabaul would target Australian controlled areas of New Guinea (April 3). The precise target was not revealed, but Commander Rochefort assessed the targets as Port Moresby and the Solomon Islands. Another decrypt revealed the presence in Truck of a carrier strike force to be used for Operation MO along with the RZP invasion force at Rabaul (April 9). This confirmed the target. British and American code-breakers had previously learned that 'RZP' was the Japanese code for Port Moresby. British code-breakers in Ceylon intercepted and decrypted the final piece of the MO puzzle (Mid-April). The British informed Nimitz that two of Admiral Nagumo's first-line carriers had been temporarily detached from the First Air Fleet--Shokaku and Zuikaku. The Allies now knew that the Japanese naval offensive would be the Coral Sea to the east of Australia's Cape York. The American carriers in the Coral Sea sank a small carrier, but Lexington was lost. Even so Shokaku and Zuikaku as a result of the were not used for the Midway operation-MI. (Actually Zuikaku with Shokaku'sair squadron could have been used, but Yamamoto thought that it was not needed. Admiral Nagumo would have only four carriers. And Station Hypo produced decrypts which gave Admiral Nimitz the information he needed for the Battle of Midway (June 1942). Despite the inexplicable appearance of the American carriers, the Japanese remained supremely confident in the security of their codes. Even a German report failed to convince the Japanese. Important American newspapers virtually announced that the Japanese codes were broken. Even so, the United States continued to read Japanese naval messages throughout the War. The ability to read JN-25 also proved useful on other battlefields, including New Guinea and the Marianas. It was the ability to read JN-25 that led to Yamamoto shoot down (April 1943). After the Guadalcanal disaster, Yamamoto organized an inspection tour to meet with front-line units and improve their morale. The Yamamoto's headquarters sent a message to a unit on Bougainville doing battle with the Americans. The message contained the precise details of the Admiral's itinerary, including the times and locations, especially the arrival at Bougainville. And Bougainville was within range of American fighters on Guadalcanal. The coded message also included the number and types of planes that would transport the Admiral. This was important because it enabled the Americans to launch the necessary force as well as to identify Yamamoto's air squadron from other Japanese aircraft.

Cracking the Maru codes (early 1943)

The principal defense of the Japanese Marus (merchant ships) was the immense size of the Pacific ocean. Intercepting the Marus, including tankers, bringing raw materials back to the Home Islands and supplies to the military forces scattered around the Pacific would have required an enormous submarine force and endless hours of fruitless patrolling. The difficulty faced by American submariners was increased by faulty torpedoes. Even when improved torpedoes reached the fleet, submariners still faced the problem of finding the tiny Marus in an immense ocean. Air patrols could cover large areas, submarines had a much more limited search range. It was the cracking of the Maru codes that made a successful submarine campaign possible. The Maru codes named the Weh-Weh code tracked Japanese merchant ship movements. Each Japanese merchant vessel was required to transmit "noon positions". This was included in the coded messages. Thus the code breakers were able to give ComSubPac the daily position of Japanese merchant vessels. The Weh-Weh was actually a 'housekeeping' and thus a level code that was not particularly secure. With this invaluable information, a relatively small American submarine force decimated the Japanese merchant marine. The U.S. Navy had 288 submarines during the War, most were deployed in the Pacific. This was a much smaller force than the German U-boat fleet which was deployed in a much smaller area. And with the destruction of the Marus, Japan lost the ability of to ship oil and other raw materials to the war industry factories on the Home Islands--the very reason they went to War. [Lewin] Japan had a large submarine force of its own. A mindset discouraging a commerce war as well as the need to supply isolated garrisons impeded a comparable Japanese effort, but the failure to crack American codes made a comparable Japanese effort impossible.

Cracking the Japanese Army codes (1943-44)

American code breakers after cracking the diplomatic Purple Code primarily focused on the JN-25 naval codes. Cracking the Maru code was another significant achievement. Little progress was made on the Army codes. This was primarily because through 1942 it was primarily the Imperial Navy that American forces were fighting. After Pearl Harbor, the American code breaking effort steadily expanded, but very little of that expanded effort was directed at the Japanese Army codes. Beginning with Guadalcanal (August 1942), the United States began engaging the Japanese Army first on Guadalcanal and then on New Guinea. Yet no progress was made on the Army codes. In fact there had been no serious effort to do so. By 1943 this was becoming an embarrassment within the code breaking community, especially at the U.S. Army's Arlington Hall facility which had the primary responsibility. The problem was that they did not know where to begin. Which shows just how important the Polish bonanza was to Bletchely Park. The Army codes began as a straight forward system, but as the War progressed became more and more complex. And this complexity stymied the small group Arlington Hall cryptologists assigned to the Army codes. As late as the Guadalcanal invasion (August 1942), only two dozen people were working on the Japanese Army codes. There first effort was what they called 'brute forcing' using an IBM machine. But the staff was expanded as was the intercept capability. From virtually nothing, the Allied cryptologists rapidly began cracking the system. The first real break came when the Arlington Hall cryptologists got their hands on four message forms (March 1943). Then Arlington Hall, the Central Bureau in Brisbane (CBB), and Bletchley Park began to detect anomalies in the intercepts which led to insights that enabled both Arlington Hall and the CBB to understand the coding system (April 1943). The staff at Arlington Hall was tripled almost overnight. Understanding the system did not mean that the intercepts could be easily or rapidly deciphered, even by the expanding staff. But progress was rapid. Here the Arlington Hall cryptologists had several breaks. The complexities of the Japanese language forced the Japanese to often use Chinese characters and here they used an existing commercial telegraphic numerical system readily available. Arlington Hall broke into the Water Transport codes (June 1943). This was the Army unit operating shipping, most supply ships. The first result was learning about a supply convoy from Palau to Wewak, which upon arrival was met by a strike force of B-25 bombers (September 1, 1943). The complexity of other codes proved difficult to master. And the Japanese made major changes (February 1944). Even so by this time the Army codes had been thoroughly penetrated. The constant changes actually helped Arlington Hall and CBB. There were so many isolated Japanese outposts that the changes had to be sent electronically in he old codes, exposing them to reception. The big break came in New Guinea. The battered and poorly supplied Japanese 20th Division after an extended battle was ordered to withdraw from Sio. Unlike American units had little transport. The soldiers decided to bury a heavy steel box rather than lugging it along. A few days later, Australian engineers using metal detectors to find mines got a scare, thinking they were standing over a massive mine. Rather than a mine, however, it was the buried box--which turned out to be a cryptological mother load. It was the entire cryptographic history of the 20th Division. [Budiansky, pp. 319-25.] Soon the Americans were reading Army messages as soon as the Japanese (Match 1944). Eventually they were reading them faster than the Japanese. Cracking the Army codes proved of immense importance to General Douglas MacArthur’s Pacific campaigns. [Drea] The Japanese Army like the Navy had ample reasons to suspect that their codes had been broken. The Japanese did take steps to ensure security, but throughout the War, they remained convinced that codes were secure. [Dreaa and Richard]

Ambassador Baron Hiroshi Ōshima

Cracking Japanese codes not only brought vital information about Japan, but also NAZI Germany. Ironically the best source of information on NAZI Germany was not a well-placed spy, but a hard-drinking but capable Japanese diplomat who was fervent NAZI-ally--Baron Hiroshi Ōshima, the Japanese Ambassador to NAZI Germany in Berlin. Ambassador Ōshima was ardently pro-NAZI and doing his best to bring Japan into the war against the Soviet Union. He developed close relations with top NAZIs and Wehrmacht commanders. Thus he had valuable insights on the NAZI war effort. The reports he sent back to Tokyo provided the Americans a wealth of information. Breaking the Japanese diplomatic codes allowed the Jerricans as part of Magic to read these reports. It was like having a spy planted among the NAZI political and military elite. The reports included a discussion of the thinking of not only Wehrmacht generals, but Hitler himself and top NAZIs. Ambassador Ōshima even toured the Atlantic Wall and described it in detail. He reported on secret weapons research, including jet engines. This was valuable because as the War situation deteriorated, the Germans became increasingly willing to share their technology to the Japanese. The Ambassador toured bombed German cities and reported that the bombing was not greatly disrupt armament production in 1943 and even early 1944. Here he was correct as far as the production numbers were concerned, but he did not provide a full picture. The Germans did maintain arms production, but this was largely because of Speer's rationalizing German industry. Had it not been for the bombing, Germany could have increased production much more. And Ōshima missed the fact that the Luftwaffe was being methodically destroyed. The Luftwaffe was also forced to pull back from France where it would not be a factor when the D-Day landings occurred.

Japanese failure to detect

Perhaps the greatest mystery about cracking the Japanese codes is how the Japanese could not have detected it. The Pacific is a huge expanse. The chances that a major enemy force should appear unexpectedly just when and where the Japanese planned operations were minuscule. This alone should have told the Japanese that when American carriers suddenly appeared in the Coral Sea just as the Japanese were staging Operation MO ti seize Port Moresby that JN-25 had been cracked. And if that was not sufficient, their appearance again to defend Midway against Operation MI should have conclusively settled the issue. This is particularly the case because of the outrage in Japan when American cytologist Y.O. Yardley published is tell-all book with details about cracking Japanese codes and how the intelligence was used against Japan at the Washington Naval Talks. One might have thought that the Japanese would have been careful to insure that this never happened again. The Japanese could not have known about Yardley in the 1920s, but the coincidences in the Pacific War, including the Yamamoto shoot down were too glaring for any competent military to ignore.

German Codes

The American focus before Pearl Harbor was understandably on the Japanese codes. Upon entering the War, the United States was given the invaluable gift of the work at Bechley Park in cracking the German Enigma. The United States brought to the table, enormous new resources to exploit what the British had achieved. Many readers believe that cracking Enigma was a simple fact and once cracked that messages could be easily read. It was much more complicated than this. First there were more than one Enigma. Each service had their own Enigmas as well as agencies like the SD and SS. And there were additional codes such as training codes. And the Germans were steadily introducing additional complications. Thus intercepted messages often required considerable work to be read. The manpower requirement was huge, especially to decrypt the messages in a time frame that made them useful. This the American work was very important. And the Americans helped increase the number of messages intercepted that could be decrypted. The American work was primarily done in the Washington, D.C. area. The Army operation was at Arlington Hall. The Navy had a separate Communications Annex on Nebraska Avenue near American University. Here they handled the vital intercepts from German U-boats. The final German code was broken (January 1945). Unlike the Japanese codes there was not an immediate py off, except in the Battle of the Atlantic. The British did not have the ground forces to fight the Germans and the Soviets ignored the British warnings of a German invasion. As the Americans began to arrive in force, the Allies gradually developed the capability to capitalize on the Ultra decrypts in ground military operations.

Italian Codes

Vichy Codes

Soviet Codes

The United States along with Finland and the Axis countries cracked some of the Soviet World war II codes. The U.S. Army's top-secret Signal Intelligence Service (SIS), the forerunner of the National Security Agency (NSA), began working on Soviet secret messages (February 1943) hoping to crack the diplomatic code. SIS code named the effort JADE, BRIDE and DRUG, but it eventually became known as VENONA. Venona is just a code name and has no geographic connotation. The project was initiated by Ms. Gene Grabeel, but military personnel soon took over the program. The Venona work was conducted at Arlington Hall. As the effort progressed the SIS obtained a range of Soviet messages. Many were from the Soviet Trade Office working with Lend Lease, but there were messages from any other agencies as well, including the military and intelligence services. From an early stage, the SIS staff determined that the messages came from five different agencies with separate encryption systems. Although the effort began during the War, the SIS dis not succeed in reading many of the messages until after the War. . Many of the messages the United States had to work with were messages associated with the Soviet Trade Office involved with Lend Lease. The first success came fairly quickly. Richard Hallock, an Army Signal Corps lieutenant and trained an archaeologist (who worked with ancient writing systems) succeeded in developing insights into the system being used by Soviet trade officials who were relatively lax in their security measures (October 1943). This provided clues to other cryptologists working on messages from other Soviet agencies. Cecil Phillips managed to develop a beginning understanding of NKVD messages (1944). This was a more difficult undertaking because the NKVD more carefully protected their messages, using double encryption. As a result, it would take 2 years of work to actually read any of the NKVD messages. The Venona was assisted after the Germans surrendered (May 1945). Army security officers were able to obtain access to the German work on Soviet codes. Meredith Garner decrypted the first portions of the NKVD messages (Summer 1946). The results were startling. It was clear by 1947 that Soviet agents had penetrated a variety of U.S. Government agencies. The British joined the effort and sent two of their cryptologists to Arlington Hall (1948). As information on Soviet espionage emerged, the Venona group contacted the Federal Bureau of Investigation (FBI). FBI Agent Robert J. Lamphere who was given access to the Venona decrypts. [Goebel] The American decrypts are today known as the Verona papers and provided insights into Soviet espionage operations in the United States.

Magic Discovered (1941)

German Charge d[Affairs in Washington, Hans Thomsen, before America entered the War was involved in serious incident promoting isolationism. He was involved in an even more serious incident. He informed the Foreign Ministry in Berlin that the American Government had broken the Japanese diplomatic (Purple) code (April 1941). Unmasking the American Magic operation of course would have been a major intelligence coup. Apparently his source was Soviet Ambassador Konstantin Umansky who benefited from the very substantial Soviet spy network in America. 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. An even more obviously that the Americans were reading the reports of the very well informed Japanese Ambassador in Berlin, Baron Oshima, which is exactly what occurred. Neither the Germans or Japanese did anything about it. The Germans presumably thought it was a Japanese matter. But in fact, Magic produced a wealth of information on the Germans as a result of Oshima's transmissions.

Lack of Discovery

An interesting question that needs to be considered is why did neither the Germans or Japanese detect that their codes had been broken. This is not to say that there were not suspicions, but apparently neither of the two main Axis powers was convinced that the Allies had cracked their codes. Some of the reasons are the same for both the Germans and Japanese, but other reasons are unique. Their is no one single definitive answer to this, but we have some ideas here and would be interested in ideas that readers may have.


Boyd, Carl. Hitler's Japanese Confidant: General Oshima Hiroshi and MAGIC Intelligence, 1941-1945 (1993), 294p.

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.

Quinto, David. E-mail message (January 15, 2019).

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).


Navigate the CIH World War II Section:
[Return to Main World War II code breaking system page]
[Return to Main World War II code system page]
[Return to Main World War II page]
[Biographies] [Campaigns] [Children] [Countries] [Deciding factors] [Diplomacy] [Geo-political crisis] [Economics] [Home front] [Intelligence]
[POWs] [Resistance] [Race] [Refugees] [Technology]
[Bibliographies] [Contributions] [FAQs] [Images] [Links] [Registration] [Tools]
[Return to Main World War II page]
[Return to Main war essay page]

Created: 5:30 AM 2/23/2011
Spell checked: 6:40 PM 1/15/2019
Last updated: 11:42 AM 2/10/2019