>>SIGSALY Exhibit

Picture of SIGSALY Exhibit SIGSALY was the first secure voice encryption system for telephones. It was invented and built by Bell Telephone Laboratories in 1943. It had several technological "firsts" including pulse code modulation for speech transmission, multilevel frequency shift keying, and bandwidth compression.

The exhibit is a mock-up of one-third of the entire system, which weighed 55 tons and consisted of forty racks of equipment. It took thirteen people to operate and required fifteen minutes to set up a phone call. The first two units were installed in the Pentagon in Washington, DC and in the basement of a popular London department store. (It was too large to fit in Churchill’s war chambers.) During and after the war, units were installed worldwide totaling twelve locations for secure telephonic communications.

SIGSALY used recordings of purely random noise for its security process. Both the sending and receiving station had copies of the acetate records and as one “encrypted” the voice, the other “decrypted.” Understandably, voice quality was quite poor, but it was secure. SIGSALY was not broken by the Axis powers.