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Book Review: Top Secret Communications of WWII, by Donald Mehl, Class 44-35

This review reproduced from and originally published in CRYPTOLOGIA magazine.
Author: Dr. Louis Kruh, Editor. Minor editorial changes have been made to bring its content current.




Top Secret Communications Of WWIIOne of the closest guarded secrets of World War II was the cloak and dagger communications system known in the Signal Corps as Sigsaly and nicknamed The Green Hornet after a popular radio program of the day that used a similar sounding buzz in the introduction to its radio program. Bell Laboratories and the Army General Staff called it the "X" system.  

The reason for the secrecy was that it used a new digital technology that made it absolutely unbreakable by an enemy. Therefore, it was used by the highest levels of military and civilian officials for strategic and tactical conferences between Washington and all of the theaters of war. It was installed and operated by the 805th Signal Service Company.             

The details of Sigsaly were kept secret until they were released under the Freedom of Information Act in 1975. With the release of the Bell Laboratories' patents and other information through the years, its contributions to the war effort and technology became known. Now, the entire story of this vital wartime facility is told in its entirety from its inception to its final decommissioning in a book called TOP SECRET COMMUNICATIONS OF WORLD WAR II, by Donald Mehl, a graduate of the Army Signal Corps OCS Class 44-35.

This book tells the story of the development, implementation, and operation of this secret telephone system and also the events surrounding the uses of the system. The story is told in the context of World War II and illustrates the impact that Sigsaly had on the major campaigns of that War. The Bell Telephone Laboratories, the Army General Staff and the Signal Corps brought this system to fruition and provided secure voice communications worldwide for U. S. military and civilian leaders.

In early meetings between President Roosevelt and Prime Minister Churchill, they expressed a need for better communications between Washington and London; they knew that the commercial overseas telephone system lacked security. In fact the Germans were monitoring it and sending transcripts to Hitler. When the opportunity came to obtain an absolutely secure radiotelephone system, namely, the Green Hornet, General George Marshall gave the project his approval and a high priority.

Donald Mehl - In front Judiciary building, Manila, WWIIThe Green Hornet signal was designed so that conversations could be carried on between distant points with complete secrecy. The transmitted information was so enciphered as to produce security against decoding in case of interception of the transmitted signals by someone not in possession of the cipher key. This means that even if someone had a duplicate set of equipment they could not decipher the signals. In fact, the Germans did intercept the radio signals but did not even recognize them as voice signals. 

The method of encoding consisted of an analytical breakdown of the speech energy into frequency bands from which control currents proportional to the energy in each band or channel were set up. These control or energy-defining currents were digitally coded, properly combined and then transmitted to the distant receiving end. At the receiving end, the energy was again divided into the component channels and the proper key applied to each. The resultant control currents actuated a synthetic voice source from which the original speech was reconstructed. Pitch as well as sibilance and the syllabic sounds of the voice were determined and included in the signal. The coding and decoding was done digitally using one-time records.

From the fighting in Africa to the Japanese surrender in Tokyo Bay, Sigsaly was present with every U. S. Army Theater headquarters. Over 3,000 top secret telephone conferences were held using Sigsaly. The buzz of the Green Hornet carried these conferences from the Pentagon in Washington D. C. to the overseas theater headquarters of the U. S. Army and Navy. U. S. leaders, military and civilian, were able to discuss the problems of war with absolute security. These daily conferences were solving the detailed problems that made possible the winning of  the war.

Its development opened the way for the digital revolution since it was the first voice product ever manufactured that used digital techniques.  The term digital was not used at that time. The technique was then known as pulse transmission; therefore, Sigsaly was credited with being the first pulse code modulation (PCM) equipment ever manufactured. Later, most telecommunications systems used this technique.            

SIGSALY - aka - The Green HornetMany men and women were involved in the invention, procurement, deployment and operation of the Sigsaly system. Many more made use of the system to prosecute the war. Development engineers at Bell Telephone Laboratories eventually received 32 patents for their inventions.  Western Electric Company built the equipment in record time. Instructors at The Bell Laboratories School for War Training taught this advanced electronic technology to the military students. The U. S. Army General Staff worked to approve, procure and implement the system in record time while imposing the tightest security possible to prevent its being compromised. The Signal Corps recruited and organized the skilled people who would install and operate the system around the world.             

Everyone involved was required to maintain the secrecy of the system, even in civilian life, for three decades after the war ended. They could not answer the question, “what did you do in World War II.”  Now, thanks to declassification and this book, the whole story can be told.             The book was written by a former member of the 805th Signal Service Co.


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Additional Notes & Clarifications By The Author, Donald E. Mehl

[Editor's Note: As of the date of this publication, June 2012, Don Mehl was approaching his 90th birthday.]

The book principally describes the two cryptographic systems used for high-level top secret conferencing during World War II by the General Staff in communicating with overseas theater commanders. It was also used by high level government officials such as the President and his cabinet for communications with their counterparts in other countries.

The SIGSALY system provided totally secure telephone conferencing facilities and the SIGTOT system provided equally totally secure instantaneous teletype communications for conferencing and the transmission of top secret information. Descriptions of other widely used encryption systems are also included in the book such as the SIGABA and M-209. A description and comparison is made with German cryptographic systems such as the ENIGMA and Lorenz. The existence and use of SIGSALY was a closely guarded secret.

Unbeknownst to many, it was a huge system. A total system could weigh up to 50 tons. It required approximately 2,000 square feet of floor space. Members of the 805th Signal Service Company, who operated the system, had to keep these secrets for many years even after the end of the war. Only those who had a need to know had knowledge of the system. While General Marshall knew of the system, he did not have clearance for the technical detail of the system because, of course, he had no need to have this knowledge. Initially only certain people could use the system and there was an official a list of those who were authorized. 

Don Mehl - SIGSALYSIGSALY operated from July 1943 until mid-1946 when it closed down and all of the outlying terminals were returned to the Army Security Agency. The technology of SIGSALY remained a secret until 1976 when Bell Laboratories, who designed the system and held many of its patents, had it declassified under the Freedom of Information Act. Many of the patents covered digital techniques that Bell Labs used in their development of digital communications. SIGSALY is known as the “Beginning of the Digital Age” and was the first digital voice product ever manufactured.

SIGTOT was used until 1959. Until then there was not a substitute for totally secure Teletype communications with one-time encryption without repetition. The 805th operated SIGTOT in the Pentagon and other locations; however, since it only required the addition of the 131B-2 Encryption Table to a standard Teletype installation it was possible to install SIGTOT in other places such as the White House. The key used was a perforated tape that was provided for each end of a communications circuit. This was a symmetrical system which limited it to high-level use because identical tapes would have to be produced for each end of every circuit. The technology and equipment for the SIGTOT system is described and illustrated in this book. When seeking background information for the book I found that the NSA did not have information about SIGTOT because everything had been destroyed. However, I was able to obtain an instruction book from the grandson of the inventor of the Teletype machine who kept an instruction book on everything that he had made. All of this information is in the book.

The SIGSALY system was installed and operated by the 805th Signal Service Company. The 805th was a most unique army organization. Its table of organization provided for 85 officers and 200 enlisted men. Why so many officers? The 805th operate 12 terminals 24 hours a day seven days a week at all of the theater headquarters around the world. Two terminals were in the Pentagon, one for Europe and one for the Pacific. The other ten terminals were operated by detachments of the 805th around the world, each with one Captain and four Lieutenants.  One Officer had to be on duty each shift as the cryptographic officer, plus other Officers for headquarters and other duties. Fifteen enlisted men performed maintenance functions and other duties.

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Credits & Notes:

Text above reproduced with minor editorial changes in order to bring it current. Editorial changes by the Managing Editor, Original text  from Cryptologia magazine, as written by Dr. Louis Kruh, Editor.

The book's title is: TOP SECRET COMMUNICATIONS OF WORLD WAR II. It is hard cover and contains 201 8X10 inch pages, over 100,000 words and includes many pictures and illustrations. It can be purchased on this website on the PX page. Payment is tax deductable as profits from the book are donated to this website's scholarship charity. Those wishing to communicate directly with the Author, Donald E. Mehl, may send eMails to the Webmaster of this website. They will be forwarded to Mr. Mehl for his consideration in reply. Thank you.

This page originally posted 01 June 2012 

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