I’ve talked before about how technology, like music players and cell phones, has gotten smaller, lighter, and more capable during the last two or three decades. But to really appreciate how far we’ve come, it’s sometimes useful to look back further still.
I have recently been re-reading Alan Turing: The Enigma, the wonderful biography of Turing by Andrew Hodges, and was struck by a short passage about some then-state-of-the-art equipment. During World War II, in early 1943, Turing made a visit to the US, in part to help coordinate use of the signals intelligence gained from the breaking of the German Enigma encryption, and in part to explore and assist with some new communications security projects. One of these, being carried out at Bell Laboratories, was to produce a secure voice telephony system for communication between the United States and the United Kingdom. In those days there were no submarine fiber-optic cables, so trans-Atlantic telephone calls had to go via radio, making them vulnerable to interception.
A system was developed, based on a technology called Vocoder originally developed at Bell Labs in the mid-1930s. This system used digitized samples of the audio signal, taken at different frequencies with an early form of pulse-code modulation, to produce an intelligible digital voice signal that required only about 300 Hz of bandwidth. The Bell Labs scientists had developed an encryption system, “System X”, which Turing inspected. It was very far from being a model of miniaturization:
A terminal occupied over 30 of the standard 7-foot relay rack mounting bays, required about 30 kW of power to operate, and needed complete air conditioning in the large room housing it.
The device wasn’t terribly energy-efficient; all that input power produced about 1 milliwatt of encrypted audio output. The great news, though, was that the system actually worked,so that FDR and Churchill were able to talk on the phone as the war developed.