A. PLAN OF INVESTIGATION
Was Bletchley Park successful in decrypting the German Enigma cryptosystem?
In 1939, during the German invasion of Poland, Polish crypto analysts escaped to England. They took with them the broken Enigma code currently in use by German forces. Throughout the war, German forces continued to depend on this system, adding improvements and changes. Allied forces broke and rebroke Enigma, based at Bletchley Park in England. The aim of this investigation is to determine the extent of Bletchley Park’s success in decrypting Enigma. The investigation will follow the German use of Enigma and the English response. An analysis of this section should show that Bletchley Park was successful in decrypting Enigma.
B. SUMMARY OF EVIDENCE
The Enigma machine was patented as a commercial cipher program in 1919. It was adopted by German forces prior to World War II. The German Navy adopted it in 1926, by the Army in 1928 and by the Air Force in 1935. In 1926, Polish intelligence officers became aware the military buildup then under way in Germany and that these new military force utilized a new cipher. By the early 1930’s, Polish forces had implemented a program to break the new code. Three mathematics students were selected for special training in cryptology. These mathematicians were able to use plans of the Enigma machine sold to the French intelligence service to create a working Enigma machine and break the code. Despite French help, until July 1939, all material regarding the broken code remained in Polish hands.
In 1939, German military forces invaded Poland. The Poles arranged for their Enigma machine and their cryptologists to be smuggled out of the country. However, German cryptologists added two more wheels to the three wheels already in place. This made Enigma messages once again unreadable. British code breakers took over from the Poles and began working out of Station X, more commonly known as Bletchley Park. Bletchley Park was founded in 1939 with the mission of breaking the German Enigma cipher. The odds against them were calculated at 150,000,000,000,000,000,000. Over 10,000 worked at Bletchley Park at the height of its activity, many of whom were draftees from Cambridge and Oxford. Despite the resources available, from 1939 to 1941 and Bletchley Park would be forced to rely on external traffic analysis.
In May 1941, British cryptologists obtained a copy of the five – wheel machine. German submarine U-110 was depth-charged by the British destroyer Bulldog off the coast of Greenland and forced to the surface. The German commander ordered his crew to abandon U-110 and set charges to destroy the craft. The charges failed to explode and British sailors immediately boarded the U-Boat and recovered a five-wheel Enigma, along with a large amount of other sensitive papers.
In 1942, Bletchley Park again developed a problem of reading German messages, though this time it was limited to submarine codes. At this point in World War II, the Battle of the Atlantic was ongoing. It became increasingly desperate for cryptologists to break the latest version of Enigma. A new variation of Enigma, named Shark had been introduced on submarines. It was not until March 1943 that Shark would be broken. Through 1944 and 1945, as World War II began to draw to a close, no new variations of Enigma were put into use, and Bletchley Park broke remaining variations.
C. EVALUATION OF SOURCES
Two of the sources used were:
Ed. R.O. Gandy and C.E.M. Yates: The Collected Works of A. M. Turing: Mathematical Logic (Amsterdam: North-Holland 1997).
This book was a compilation of Alan Turing’s work on projects like the breaking of Enigma. As well as Turing’s papers and notes, the editors included relevant information on Enigma. The origin of most of the book is Turing’s work, which was seized by the British government in two parts. The first was immediately after World War II and the second followed Turing’s death. This volume was published with the purpose of making recently declassified material available. It is valuable as a source of information on the methods employed to break Enigma, as well as the impact of those methods. It is limited by the assumption that the reader has a grounding in mathematics.
The Shadow War (Alexandria: Time-Life Books 1991) 138-147
This book documents espionage, codes, etc. used by Nazi Germany during World War II. One chapter focuses specifically on the Enigma machine. It documents uses, modifications, how it was broken and other details. The origin of this document is as an historical evaluation of Nazi techniques, with the purpose of examining those techniques from a modern point of view. The main value of this book is detailed information of specific modifications of Enigma. However, it is limited by a lack of comparison, which was the author’s stated goal.
D. ANALYSIS
Bletchley Park’s effort to break the German crypto system Enigma were successful. Despite changes and improvements made to the system, Allied code breakers kept up with the changes and rebroke Enigma several times.
At the beginning of World War II, Polish crypto analysts had already broken the main Enigma encryption used by German forces. When Polish intelligence forces escaped from the German invasion, Allied intelligence efforts were concentrated in Bletchley Park. This provided Bletchley Park the resources necessary to attack variations of the Enigma system.
There were several periods during the war that Bletchley Park was unable to read Enigma intercepts of certain variations. Through a variety of methods, including mathematical analysis, computer decryption and the capture of German equipment, Bletchley Park regained their advantage over Axis forces.
After March 1943, and the decryption of the Shark variation of Enigma, no new modification to the system prevented Bletchley Park from interpreting German messages for a lengthy period of time. Instead, Bletchley Park was able to continue decoding messages while breaking other, minor variants of the Enigma system.
German forces were confident in the Enigma crypto system. It had been tested with almost a decade’s use in the commercial field before use by the German military structure. Despite that fact, Poland’s limited intelligence service was able break the basic Enigma system. Bletchley Park was able to expand upon that information and continue to read versions of German codes throughout the war. Towards the end of the war, Bletchley Park was able to read most German messages, helping the Allies to win the war, despite the astronomical odds against breaking the Enigma encryption.
Bletchley Park’s information did not provide them with omniscience, though. British leader Winston Churchill was once accused of withholding information learned through broken Enigma messages. According to accusations, this information stated that the English town of Coventry was to be bombed by German forces and Churchill allowed Coventry to be bombed to protect the knowledge that the Enigma system had been broken. This rumor was untrue. At the time, most German messages discussing the possibility of a raid used a variant of Enigma that Bletchley Park had not broken. Information available indicated that London was to be the target of the raid. Bletchley Park did not have access to all Enigma messages, which made it difficult to extract the specific information necessary. Within those limitations, Bletchley Park was able to gain ground against German forces. However, it is important to note that Bletchley Park was not above drastic measures to protect the knowledge that the Enigma system had been broken.
E. CONCLUSION
Bletchley Park was successful in decrypting the German Enigma cryptosystem, despite difficulties. A key problem was the fact that Enigma was not the sole code; instead it was a system upon which many German encryptions were based. They faced setbacks as German forces modified and adapted Enigma machines, but specific variations were broken one after another. Despite long periods, during which specific variants were not translatable, Bletchley Park was able to still understand information from other sources and remain informed.
F. LIST OF SOURCES
Bury, Jan. Enigma – A Polish View. (Warsaw, Poland: Crypto 2001)
Ed. R.O. Gandy and C.E.M. Yates: The Collected Works of A. M. Turing: Mathematical Logic (Amsterdam: North-Holland 1997).
The Shadow War (Alexandria: Time-Life Books 1991) 138-147
www.bletchleypark.org.uk
