SIGSALY

Secure Communications Need

The intense desire for the Allies' secure communication during World War II was actually the pioneering step that began a chain of digital enhancements all the way up to how we communicate today with digital video, wireless phones, etc. On the morning of December 7, 1941, the U.S. Army Chief of Staff, General George C. Marshall received information regarding Japan giving up on a political solution with its relationship with the U.S. So, General Marshall wanted to quickly notify U.S. Pacific commands of this and to be ready for anything. However, General Marshall wanted to send this vital message in secret but was suspicious of the secure means to do so at the time. Usually, the securest means at the time was to use the A-3 Scrambler, which was based on older 1920's technology. Even though General Marshall did not know it at the time, the Germans had cracked the A-3, thus were continually interpreting and reading messages from President Franklin Roosevelt and other world leaders at the time. Ultimately, although General Marshall smartly didn't use the A-3 but instead used the means of a coded radiotelegraph. Unfortunately, the message made it after the attack.

Bell Telephone Laboratories

Around 1936, the BTL began experimenting with converting analog signals to digital data. Many attempts to successfully do so and have an intelligible voice on the other have failed. By 1942 the U.S. Army was awarded a contract with BTL, headed by A. B. Clark who later worked for the NSA, to develop such a system. Alan Turing one of the significant figures at Bletchley Park at the time, assisted Clark in this project. Finally, after many months, by July 1943, the project was a success. They originally named the new system "The Green Hornet" because of the buzzing noise that would occur during communication, which indicated that someone was trying to eavesdrop on the conversation. They then changed the name of this large electronic machine to SIGSALY. The name was not an acronym but just a random code name. Amazingly enough, this was patented and remained a secret all the way up until 1976. So the BTL was the first to invent digital voice that was encrypted and a means to transfer it securely.

IEEE Acknowledgments

The IEEE attributed 8 firsts to SIGSALY [7d]:

1. The first realization of enciphered telephony.

2. The first quantified speech transmission.

3. The first transmission of speech by Pulse Code Modulation (PCM).

4. The first use of companded PCM.

5. The first examples of multilevel Frequency Shift Keying (FSK).

6. The first useful realization of speech bandwidth compression.

7. The first use of FSK - FDM (Frequency Shift Keying-Frequency Division Multiplex) as a viable transmission method over a fading medium.

8. The first use of a multilevel "eye pattern" to adjust the sampling intervals (a new, and important, instrumentation technique).

SIGSALY System Overview

Physical Characteristics

The entire terminal of a SIGSALY had on average 40 racks of electronic equipment. They were very large and heavy, so much so that it had to be readjusted every time to its environment that it was housed in. Furthermore, each SIGSALY consisted of various electromechanical equipment such as turntables, relays, vacuum tubes and synchronous motors, along with large cooling systems for managing generated heat.

Locations

The SIGSALY found its home in various places throughout the war, such as Australia, North Africa, Manila, Guam, Hawaii, Paris and in London and Washington, D.C. London's SIGSALY was located in an annex to Selfridges Department store. However, Churchill was able to access it from the Admiralty Building about a mile away. On the other end of the Atlantic, Washington's SIGSALY was located at the Pentagon which was just built in 1943. President Roosevelt originally had it in the White House but because of Churchill's erratic calling at all hours of the night, amusingly enough, Roosevelt had it moved to the Pentagon. Now, the Allied cryptographic service was able to adhere to its 2-pronged "provide and protect" motto. Overall, SIGSALY supported roughly 3,000 secretive conversations. Once the Germans noticed A-3 signals were decreasing they realized that another means of communication was taking place. Thus, one of the German Deutsche Reichspost members later said "there is not much to be gotten from them now."

Maintenance

The maintenance for the SIGSALY was a significant task. The Western Electric Company provided detailed specifications on its use. Normal usage time was 8 hours a daily where the balance of the time was for maintenance. Vacuum tubes were often checked, power supplies and stepper circuits were constantly being adjusted. Despite the complexity, the members of the 805th Signal Service Company, Army Signal Corps, who operated the SIGSALY in Washington and various places, were efficient and had barely any downtime.