*** World War II -- American Country Code Breaking Efforts-Army Signals Intelligence Service/Navy Code and Signal Section

World War II: American Country Code Breaking Efforts-Army Signals Intelligence Service/Navy Code and Signal Section

Freidman cryptology
Figure 1.--A major figure in American cryptology in both World War I and II was Wiliam Friedman. He was credited for virtually created American cryotology from scratch after America entered World War I. He was a leading figure in crascking the Japanese Purple Code during World Warv II. Less well known is that the Friedman's were a husband and wife team. His wife Elizabeth in fact was a major factor in Willian develooping cryptological skills in the first place and in the cryotological guide book explaining methids they develooped. Elizabeth had many accomplishment of her own, helping the Coast Guard crack the codes used by Prohibition Era liquor sugglers. When this phiotograph was taken, Elizabeth had just finished court testimony that desroyed the smuggling operation. The Coast Guard assigned a priotection squad to her and put her in charge of a cryptological unit. After Pearl Habor, her unit was folded into the Navy's cryptological effort. Elizabeth focused on German spies in South America that were providing intelligence to U-boats on shipping.

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 U.S. Army took over the Black Chamber files and established its own code-breaking group, the Signals Intelligence Service within the Signal Corps directed by William Friedman (1921). Friedman was a key figure in American cryptology, basically creating an American cryptological capability from scratch after the country entered World War I. He played a key role in both World War I and II, most famously helping to crack the Japanese diplomatic codes. He was the main figure in building a machine that could read Purple messages faster than the Japanese could read the messages. Not fully understood is that the Friedmans were a cryptographic husband and wife team. His wife Elizabeth had in fact helped develop William's Cryptographic skills and the principles of cryptoanalsis used by the first American icebreakers. 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 beyond what William and Elizabeth Friedman had developed at Riverbank during the War. Incredibly, the reason that the Friedman's had rudimentary cryptological skills is that a weaklthy industrialist had hired them to crack codes he believed were present in Shakespearean texts to prove the true author was Roger Bacon.

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 cryptonalysts' (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. Elizabeth joined her husband as a junior partner, but as her abilities were not fully recognized, after a year resigned and focused on their two young children who arrived shortly. SIS was gradually expanded as the Japanese moved toward war in the Pacific. The American focus was on Japanese codes. With these limited resources Friedman and his team managed to crack the Japanese diplomatic (Purple) code about a year before Pearl Harbor (September 1940). The strain, however was enormous and he had a nervous breakdown. Elizabeth devotedly helped nurse him back to health, although he was never the same. The resulting decrypts became known as Magic. Pearl Harbor of course changed everything. Suddenly vast resources were channeled into code breaking. SIS worked with British units in the Pacific also working on Japanese codes. 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 Purple/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 organization 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.

Coast Guard Efforts

Elizabeth Freidman thought that she had left the world of code breaking behind. The 18th Amendment had led to Prohibition (1920). And smuggling liquor had become big business. And the Coast Guard with its small budget was being overwhelmed. Then one day a Coast Guard officer came calling (1925). He explained that the Coast Guard network of radio towers were picking up thousands of radio messages, but could not decipher them. They were such simple codes, Elizabeth was able to do it easily. The Coast Guard put her in charge of a Code Breaking unit that helped break up major smuggling operations. She not only deciphered the messages, but developed details on who was running the operations and details about the operations. This include the Capone organization. Elizabeth's court testimony was front-page news all over the country. The Coast Guard set up a protection unit to protect her, afraid that the gangsters might target her. After Pearl Harbor, the Coast Guard unit was folded into the Navy's operation. A Navy officer was put in charge of her unit. The unit focused on German intelligence operation in Latin America. They were providing the German U-boat fleet details on ship sailings from South American ports. Her unit was instrumental in disabling the German intelligence operation. She was unable to talk about her work. J. Edgar Hoover issued press releases claiming that the FBI was responsible. All of Elizabeth's work was unknown until World War II records were finally declassified (2008).

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 work 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 an instrument 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】


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.

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

Yardley, Herbert O. The American Black Chamber (1931).


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Created: 10:01 PM 11/12/2016
Last updated: 2:42 AM 12/7/2023