[Popular Mechanics] has an interesting article about Alan Turing’s nearly-forgotten speech encryption device. Codenamed Delilah, it was in many ways an early form of digital encryption. It was secretly developed alongside his most famous wartime achievement of breaking the encryption used by the Nazis’ Enigma machine; itself a remarkable device we’ve covered in detail in the past.

Delilah was developed at a separate location, and Turing worked with a young electrical engineer by the name of Donald Bayley who not only helped Turing implement design concepts and theory as practical circuitry, but took copious notes of their work and discussions. His documents, which went up for auction a few years after his death in 2023, reveal a first-hand account of their work.

Back then, a vocal encryption system did exist. Bell Labs had developed SIGSALY, a seriously top-secret system that provided encrypted voice communications at the highest levels. But one of SIGSALY’s biggest drawbacks was that it was absolutely monstrous.

Delilah did the same job, but was portable and battery-powered. Delilah was three small boxes weighing around 39 kg, and it’s hard to overstate just how remarkable of a feat of miniaturization this was. However, by the time Delilah was wrapped up, the war was over and the project wound down without ever being produced or deployed in any meaningful way.

Encrypted communications is standard stuff today, but back then there was simply no need for a vocal encryption system in peacetime. The reason we know what we do today is thanks mainly to the effort Bayley put into documenting things.

It again demonstrates that if the people involved don’t write things down while they know it, that knowledge can simply disappear. Sometimes people make the effort and the rest of us benefit, like with the Delilah project and also with the history of liquid rocket propellants — a dry-sounding topic that we assure you is anything but.