© Mark Ollig
In 1942, under contract with the US government, AT&T Bell Telephone Laboratory engineers began working full-time to develop a top-secret voice encryption system to ensure the privacy of telephone conversations between WWII Allied commanders at the highest level.
These commanders included the President of the United States, Franklin D. Roosevelt, and the Prime Minister of Great Britain, Winston Churchill.
During this time, the world's first electronic digitally-encrypted speech encipherment device was built by Western Electric, the manufacturing arm of AT&T, under the project name The X System and Project X.
It became officially known as SIGSALY, a secure encrypted voice full-duplex electronic transmission terminal system using pulse code modulation techniques to encode analog audio signals digitally.
SIGSALY was not an acronym but a confidential, secret military cover name resembling an acronym. Many Army Signal Corps name abbreviations began with SIG.
It was later called "The Green Hornet" after the radio program of the same name because of the buzzing noise induced on the telephone line by anyone attempting to eavesdrop during the transmission of an encrypted conversation.
Physically, a SIGSALY terminal was a massive voice encryption/decryption computing system weighing 50 tons and containing 40 metal racks of equipment cabinets filled with wiring and electronic components, including 384 thyratron hydrogen/deuterium gas-filled vacuum tubes and radio transmitting and receiving equipment.
It also included two voice transmission phonograph record/disc precise turntables synchronized on both the sending and the receiving end via a timing signal from the US Naval Observatory.
SIGSALY, an enciphered telephony computing system, consumed 30,000 watts of power, generating a lot of heat, and required a heavy-duty air conditioning system housed in a separate room.
It was also equipped with a full-duplex voice link using narrow-band high-frequency channels over shortwave radio.
The encryption system analyzed human speech at 50 times per second and clipped voice conversation into 20-millisecond intervals. The analog frequencies (human speech) were sampled, modulated, digitized, coded, and then transmitted to the receiving end that would decode and reconstruct the original human speech pattern.
The 805th Signal Service Company of the US Army Signal Corps completed the installation of the SIGSALY system in July, 1943.
The first official transatlantic encrypted telephone call using SIGSALY occurred between the Pentagon and London July 15, 1943.
US President Franklin Roosevelt and British Prime Minister Winston Churchill regularly held encrypted private telephone conversations transmitted across the Atlantic Ocean using SIGSALY.
The White House in Washington DC had a voice-encrypted extension telephone line cabled from the Pentagon, three miles away.
Each SIGSALY terminal required 13 people to operate, and it took 15 minutes to set up a secure encrypted telephone call.
At the cost of $1 million apiece in 1943 ($17 million today), each SIGSALY terminal could communicate with any terminal connected to the system to establish, relay, and transmit an encrypted conversation to and from any other terminal location.
There were 12 confirmed SIGSALY terminal locations built and installed worldwide.
During the 1940s, the filed US Patents for technology used with SIGSALY were kept secret and not publicly viewable.
The military kept details about SIGSALY classified as top-secret for decades, including its 32 US Patents.
I am listing four US patents directly related to SIGSALY, including the initial patent filing date and when the patent was officially granted through the United States Patent and Trademark Office: US Patent 3,024,321 Dec. 29, 1944 - March 6, 1962; US Patent 3,373,245 Aug. 27, 1942 - March 12, 1968; US Patent 3,897,591 Aug. 27, 1942 - July 29, 1975; and US Patent 3,985,958 Dec. 18, 1941 - Oct. 12, 1976, which is titled “Secret Telephony.”
For the most part, the patents remained classified and not fully disclosed until 1976, when the US Government officially declassified them and the top-secret status of SIGSALY.
Throughout World War II, SIGSALY proved impenetrable to having any of its high-level encrypted communications intercepted and descrambled by the enemy.
I found a list of 37 names from the US who worked on the SIGSALY project, including mathematician and computer scientist Alan M. Turing from the UK.
AT&T Bell Lab engineers and scientists developed and produced many new technologies and electronic devices used during the war years from 1941 to 1945.
By the end of WWII, AT&T Bell Labs and Western Electric were at the peak of their engineering, development, and manufacturing prowess.
From the late 1940s through the 1970s, they remained, in my opinion, the most innovative technological resource in the world.
Throughout World War II, SIGSALY transmitted more than 3,000 high-level encrypted telephone conversations among Allied commanders until its removal from service in 1946 as part of the demobilization process, which destroyed much of the encryption system. However, some terminals and equipment are still in storage.
The digital quantization of speech communications using pulse code modulation on the telephone switching platforms I have worked with is a result of the technology obtained from the SIGSALY project.
