Photos of components of the U.S. Army SIGSALY digital voice encryption system used during WWII. Photos were submitted by Donald E. Mehl, Signal OCS graduate of class 44-35. Don wrote two excellent books on the subject of war time encryption. You can find them by clicking here

For the SIGSALY system the encryption process involved having pulses from the digital voice equipment mixed with random pulses that had been recorded on a 16 inch record. With duplicate records at both ends of the circuit the original voice was restored and only the parties at each end were able to understand each other and have complete security.

Shown here, a random digital key record. Records could be either acetate or vinyl, and  ran for 12 minutes each.

For comparison a modern 5 inch compact digital disk (CD) is shown that will play for an hour.

SIGSALY turntables and disks. The 16 inch records were run on standard professional turntables. SIGSALY turntables and disks
A view of one end of a SIGSALY terminal that converted an unencrypted voice signal to an encrypted digital signal. SIGSALY Terminal
A replica of a SIGSALY terminal was constructed and is on display at the National Cryptologic Museum at Ft. George Meade, Maryland. Don Mehl is shown at its dedication in the year 2000. Don Mehl at SIGSALY display, Ft. Meade, 2000