Codebreaking in World War II

Codebreaking in World War II – Review Essay

Arthur C. Winn

The three books reviewed here cannot be readjust once–not if the reader wants to gain the most complete picture of American and British activities (independent, competitive, and cooperative) with regard to World War II codebreaking. Nor if the reader desires an understanding of the interrelationships, and at times lack thereof, among the military services and the various American and British government agencies which were, or wanted to be, directly involved in codebreaking. As the authors clearly show, the interrelationships were at times cooperative, at times marked by bureaucratic internecine warfare.

Stephen Budiansky is a correspondent for The Atlantic. He received a master’s degree in applied mathematics from Harvard and has worked on classified military studies as a Congressional Fellow. The theme in his Battle of Wits: The Complete Story of Codebreaking in World War II is in the subtitle of his book. This work is comprehensive and thorough. Only time will tell if his story is “complete” in the absolute sense of the word.

David Alvarez is a professor of politics at Saint Mary’s College of California. His research for his book Secret Messages: Codebreaking and American Diplomacy, 1930-1945 was completed while he held an appointment as a scholar-in-residence at the National Security Agency’s Center for Cryptologic History. The principal theme is an appraisal of the role of codebreaking in the formulation of diplomatic policy. As the author notes, the opening date coincides with the creation of the US Army’s Signal Intelligence Service (SIS), so his book is also an operational history of SIS. He does not address codebreaking in the military or naval spheres.

Maurice Freedman served in the Royal Air Force (RAF) Bomber Command No. 100 (Special Signals) Group during World War II. After the war he pursued a career in public administration, teaching, and journalism. He has been a regular lecturer on Ultra (Enigma-based intelligence) and related issues. The theme in his Unravelling Enigma is the codebreaking carried out at Bletchley Park, the wartime home of Britain’s Government Code and Cypher School. Freedman refers to it as “Britain’s greatest twentieth-century achievement,” the essence of which was decoding and intelligence processing on an industrial scale.

All three authors emphasize that people were the key factor in the codebreaking efforts in Britain and the United States. They identify key personnel and provide examples of their contributions. Freedman notes that the results achieved were founded on “previous experience, mathematics, language, and psychology, as well as some bright ideas, and were nothing if not shrewd, well-informed, and intelligent.” The people “were drawn from a section of society loosely called ‘intellectuals,’ not a group particularly favoured by the military.” At times he refers to them as “boffins,” an essentially British term probably best defined as a government scientific technician who appears unconventional or absent-minded.

Most of those involved had little or no prior experience with cryptology. Alvarez mentions a 24-year-old math teacher who accepted a position as a junior mathematician with the US Army Signal Intelligence Service. He had no idea of what a junior cryptanalyst did, but he knew what a crypt was and guessed that the job had something to do with military cemeteries: The young man, Frank Rowlett, was later to head the General Cryptanalytic Branch at Arlington Hall.

Although Alvarez’s focus is the period from 1930 through the end of World War II, he does highlight some earlier episodes–as early as the American Revolution. These episodes suggest an amateur and unsystematic approach to codebreaking that characterized American activities in the field well into the 20th century. He writes, “No one in Washington thought that the interception and decryption of secret messages was sufficiently useful to the United States government to require some system and organization.” At least not until June 1917 when the US Army established a cipher office, known as MI-8, in its Military Intelligence Branch. The office was entrusted to Herbert Yardley who, as Alvarez and Budiansky show, became both famous and infamous.

Alvarez notes that despite MI-8’s successes in solving foreign diplomatic codes during World War I, there is no evidence that this had any effect on American diplomacy during the war or during the Versailles Peace Conference. He attributes this to President Wilson’s distaste for espionage and his resistance to the influence of any intelligence, let alone that from intercepting diplomatic traffic.

Following World War I, the Cipher Bureau (perhaps more widely known as the American Black Chamber) was created with funding shared by the War Department and the State Department. The high point in its history occurred during the Washington Conference on the Limitation of Armaments in November 1921 when the Cipher Bureau provided the US Secretary of State advance information on Japan’s negotiating strategy.

After the Washington Conference, Japan was the only significant power whose messages were regularly read. Alvarez and Budiansky highlight the problem as one of intercept. Without message traffic, the most skilled analysts are helpless. During the war, censorship on all international communications and copies of all foreign diplomatic cables entering or leaving the United States had been automatically provided to MI-S by the censorship authorities. After the war, these sources of raw traffic stopped. State Department funding was also stopped by US Secretary of State Henry Stimson, who believed it was inappropriate for the State Department to engage in covert activities of any sort. The American Black Chamber ceased operations in May 1929.

In April 1929, the Military Intelligence Division, the War Plans Division, and the Signal Corps agreed on a plan to consolidate the Army’s code compilation and code solution activities in a new Signal Corps unit, the Signal Intelligence Service (SIS). William Friedman was appointed principal cryptanalyst and effective director of the SIS. Both Alvarez and Budiansky trace the development of SIS and its activities through the end of World War II.

David Alvarez sums up his view of codebreaking and American diplomacy during this critical period in his final paragraph:

The President’s failure to grasp the diplomatic advantage proffered by signals intelligence would have marginalized the codebreakers even if their efforts had not been constrained by operational difficulties. Together, the various factors ensured that, for all its expansion and achievement, signals intelligence would have little appreciable impact on American diplomacy in the period 1930-1945.

Maurice Freedman notes that successful decoding during World War I led to the creation of the Government Code and Cypher School (GC&CS) as an interservice organization (due to the disastrous lack of cooperation in intelligence matters during the war). He writes that the name was “probably devised by some Foreign Office wag.” Budiansky notes that the name was “dreamed up” by the head of the Foreign Office’s Communication Department, Courtenay Forbes.

Both Freedman and Budiansky provide examples of agreements and disagreements over the handling of the deciphering/decoding of diplomatic and military intelligence. They also address the relationships between GC&CS and the service intelligence directorates–which at times, as Freedman describes it, “was one of stalemate.”

Freedman and Budiansky also cite operational examples in which Ultra, as well as direction finding and traffic analysis, was used with and without success throughout World War II, in North Africa, in Europe, during the Battle of the Atlantic, and in countering U-boat operations. They also cite examples where commanders chose not to believe the signals intelligence. For example, Budiansky in his comments about the Battle of the Bulge notes that Ultra had provided ample warnings of the German attack. However, the Allied generals who looked at the situation as professional military men had concluded that the German army was simply too battered to go on the attack, a view held by the German generals as well. It was Hitler who disagreed with both and ordered the attack.

Budiansky also addresses US codebreaking operations against the Japanese. He examines the Japanese diplomatic Purple cipher (intelligence from it was codenamed MAGIC) as well as the Japanese Fleet General Purpose Code. The author notes that intercepted Purple messages of 3 and 6 December 1941 indicated that Japan was about to go to war with the United States. However, not a single Japanese Fleet message (which would have contained details) was read by the time of the Pearl Harbor attack. Following the war, when cryptanalysts examined the unread traffic, they found some of the details. Although none of the messages specifically mentioned Pearl Harbor, Budiansky points out that had the pre-Pearl Harbor Japanese Fleet traffic been decoded and read at the time, it would have certainly conveyed heavy hints about the attack. That it was not decoded was partly a matter of manpower and partly one of priority. MAGIC was such a dazzling find that it blinded its possessors to possible attack information that lay buried among Japanese Fleet supply orders and maneuvers. Lesson to be learned: Consider the potential ramifications of priorities.

The Japanese Fleet Code was broken in March 1942. Budiansky provides an excellent summary of the key role it played in the Battle of Midway in June 1942 and of the relationships of key individuals-i.e., Commander Joseph J. Rochefort, Station Hypo officer in charge; Captain Edwin Layton, Pacific Fleet intelligence officer; and Commander John H. Redman, in command of OP-20-G. According to Budiansky, Redman at first claimed that Rochefort was wrong in identifying Midway as a Japanese target and then after the battle tried to claim sole credit. As Budiansky writes, “The denouement of the Battle of Midway was not one of the US Navy’s finest hours.”

Budiansky and Freedman address the functioning of the Enigma machines and the various aids and machines used in codebreaking. They include pictures and excellent appendices. Budiansky’s Appendix A provides an excellent chronology of cryptanalysis-related events from 1923 until the surrender of Japan in 1945. Readers who are cryptologists will appreciate the talent that went into developing the machines; readers who are not will find themselves grabbing a pencil and paper and working through the examples they provide.

These three books are not the first to address codebreaking during World War II. And they certainly will not be the last to do so. But together they do highlight some areas for the reader’s consideration: analytical aptitude, knowledge databases, linguistic skills, machine translations, statistical security, enemy and friendly operating procedures, interpretation and evaluation of incomplete signals information, diplomatic and military operational use, source protection, measurements of success. Questions and the answers in each of these subject areas will forever be related to the conditions and attendant circumstances at particular moments in time.

The Reviewer: Colonel Arthur C. Winn, USA Ret., has worked for the past 20 years for civilian professional service firms as a program manager and senior analyst on DOD- and Army-sponsored targeting and intelligence systems programs. He retired from the Strategic Studies Institute at the US Army War College in 1979 after more than 30 years of active service as a Corps of Engineer, Special Forces, and Military Intelligence officer, with tours in Japan, Korea, Vietnam, Germany, and as the Assistant US Army Attache in Israel.


Alvarez, David. Secret Messages: Codebreaking and American Diplomacy, 1930-1945. Lawrence: Univ. Press of Kansas, 2000.

Budiansky, Stephen. Battle of Wits: The Complete Story of Codebreaking in World War II. New York: The Free Press, 2000.

Freedman, Maurice. Unravelling Enigma: Winning the Code War at Station X. South Yorkshire, Eng.: Leo Cooper, Pen & Sword Books, 2000.

COPYRIGHT 2001 U.S. Army War College

COPYRIGHT 2004 Gale Group